JP4989305B2 - Optical pickup - Google Patents

Description

  The present invention relates to an optical pickup that irradiates a recording surface of an optical disc with a laser beam for recording or reading information.

  Optical pickups used in various optical disk drive devices for reading optical information recorded on optical disks such as CDs (compact disks) and DVDs and writing optical information to optical disks are generally emitted from a laser light source. The laser beam is converged on the recording surface of the optical recording medium.

  By the way, the size of each pit recorded on the recording surface of the optical disc is in the order of the wavelength of the laser beam used for the optical disc in order to maximize the recording density of the optical disc. Therefore, as the imaging performance of the objective lens used in such an optical pickup, a wavefront aberration (RMS <0.07λ) that satisfies an allowable value called a so-called Marechal limit is required, and spherical aberration that is a component thereof is required. Astigmatism and coma also need to be corrected well.

By the way, at present, in order to reduce the weight of the entire optical pickup and suppress the manufacturing cost, a plastic aspherical single lens is mainly used as an objective lens of the optical pickup for DVD and CD. On the other hand, in the Blu-ray Disc standard which is the next generation DVD (Digital Versatile Disc), an objective lens with NA of 0.85 is required.
JP 2006-079671

  However, when the NA of a plastic aspherical lens is increased, the ratio of astigmatism and coma generated due to system manufacturing errors and assembly errors increases. In order to prevent the occurrence of such aberrations, it is only necessary to prevent a causative error. However, an increase in cost is inevitable if manufacturing is performed with a very high accuracy.

  Accordingly, an object of the present invention is to provide an optical pickup device that can actively cancel and correct aberrations caused by the system by causing aberrations of opposite polarities to occur in the objective lens itself.

  The present invention employs the following means in order to solve the above problems.

That is, an optical pickup according to the present invention is an optical pickup that irradiates a recording surface of an optical disc with laser light emitted from a laser light source, and is an objective that converges the laser light emitted from the laser light source onto the recording surface of the optical disc. A lens and a pair of heaters arranged side by side in the track row direction of the optical disc and the objective lens sandwiched between the objective lens and the objective lens to heat the objective lens by generating heat by being supplied with an electric current; Provided between a pair of heaters arranged side by side in the pit row direction of the optical disc, the laser light source and the objective lens, and guides the laser light emitted from the laser light source toward the objective lens The reflected light of the laser beam reflected by the recording surface of the optical disc and transmitted through the objective lens is reflected from the laser light source. A beam splitter for separating the optical path of the laser beam, said about the optical axis of the objective lens, interposing a pair of light receiving regions of the optical axis arranged in the track column equivalent direction, the other pair of light receiving regions Has a light receiving element having four light receiving regions divided so as to be arranged in a direction equivalent to the pit row direction across the optical axis, and a tracking error based on a light receiving amount detected in each light receiving region in the light receiving element A focus error signal value in a state where the amplitude of the tracking error signal is maximized and a value of the focus error signal in a state where the amplitude of the reproduction signal is maximized. as for the difference, and a control circuit for detecting the distribution of the phase, receiving the reflected light split by said beam splitter Accordingly, the phase detection means for detecting the phase distribution in the beam cross section of the laser beam converged by the objective lens, and the phase of the objective lens is advanced from the other direction by the phase detection means. and selectively supplying the current supply circuit a pre-SL current to heater disposed in the same direction as the detected direction and have, characterized by comprising.

  If comprised in this way, the phase distribution in the beam cross section of the laser beam inject | emitted from an objective lens and irradiated to an optical disk will be detected by a phase detection means. The current supply circuit supplies a current only to the heater arranged in the same direction as the direction in which the phase is advanced in the phase distribution detected by the phase detection unit with respect to the objective lens. Then, the objective lens is partially heated by the heater. That is, heating is performed only from the direction detected as the phase is advanced. In the portion heated in this manner, the refractive index of the medium of the objective lens is lowered, so that the phase in the portion of the objective lens itself is delayed. Since the phase delay of the objective lens itself cancels the phase advance of the laser beam, as a result, the phase distribution of the laser light emitted from the objective lens is reduced.

  According to the present invention, it is possible to actively cancel and correct aberrations caused by the system by causing aberrations of opposite polarities in the objective lens itself.

  Embodiments of an optical pickup according to the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an optical disc drive apparatus according to an embodiment of the present invention. As shown in FIG. 1, this optical disc drive apparatus includes a thin box-shaped casing 1 incorporated in a casing of a personal computer, a video recorder, etc. (not shown), and a tray 2 that can be advanced and retracted from the casing 1. Is made up of. When the tray 2 is pulled out from the casing 1, the optical disk D can be attached and detached. When the tray 2 is pushed into the casing 1, the optical disk D is accommodated in the casing 1 and the opening of the casing 1 is closed. Furthermore, in this example, in order to reduce the thickness of the entire optical disk drive device, the tray 2 incorporates a spindle 3 and a carriage 4 which are main components for exhibiting the original function as the optical disk drive device. ing. In addition, as a thin optical disk drive device employed in a so-called notebook personal computer, there is one in which a spindle 3 and a carriage 4 are incorporated in a casing side, and an upper surface of the casing is freely opened and closed by a lid. The present invention can be applied even to an optical disk drive device.

  In the optical disk apparatus shown in FIG. 1, on the upper surface of the tray 2, there is formed a disk mounting portion 2a that is recessed in accordance with the circular outer edge of the optical disk so that the optical disk D can be mounted and rotated. Yes. A spindle 3 is embedded in the center of the disk mounting portion 2a. The spindle 3 is rotated by a built-in direct drive motor with a shaft inserted into a hole drilled in the center of the optical disc D and clamped. As a result, the spindle 3 can rotate the optical disk D.

  The carriage 4 incorporates an optical pickup, and two rails 5 and 6 are provided in a substantially rectangular notch 2b formed in the bottom surface of the disk mounting portion 2a along the radial direction with the spindle 3 as the center. Is slidably held. That is, the rails 5 and 6 are notched in parallel (and therefore in parallel with each other) in a single movement locus oriented in the radial direction around the spindle 3 on which an objective lens 7 to be described later moves. 2b. One rail 6 passes through a pair of guide followers 4 a protruding from one side edge of the carriage 4, and a fork 4 b protruding from the other side edge holds the other rail 5. As a result, the carriage 4 slides in the notch 2b so that an objective lens 7 described later moves in the radial direction around the spindle 3 (that is, the tracking direction of the optical disc D). Although not shown, a rack is formed at the tip of the guide follower 4a, and a worm gear meshing with the inner surface of the notch 2b facing the rack is incorporated in parallel with the rail 6. ing. Therefore, the position of the carriage 4 is controlled by rotating the worm gear (not shown) by the tracking motor 27 shown in FIG.

  A window 4 d for exposing the objective lens 7 included in the optical pickup is formed in the upper surface of the carriage 4, and a cavity for accommodating the optical pickup is formed inside the carriage 4.

  2 shows an optical configuration of each optical component constituting the optical pickup built in the carriage 4 (however, the illustration of the reflecting member such as a reflecting mirror and the refractive member such as a prism is omitted, and the optical path is linearized. And a block configuration of the control circuit.

  The optical components constituting the optical pickup are a laser light source 8, a beam splitter 9, a collimating lens 22, an objective lens 7, a sensor lens 25, and a light receiving element 26.

  A laser light source 8 as a laser light source emits a laser beam in a blue-violet band (405 nm) in accordance with the standard of the Blu-ray disc.

  The beam splitter 9 is held in the optical path of the laser light emitted as the divergent light from the laser light source 8, transmits the laser light, and reflects the reflected light reflected by the optical disk D toward the sensor lens 25. It is a prism (polarization beam splitter).

  The collimating lens 22 is a positive lens that refracts the laser light emitted from the laser light source 8 and transmitted through the beam splitter 9 so as to convert the divergent light into parallel light.

  The objective lens 7 is a condenser lens (positive lens) that focuses the laser light transmitted through the collimator lens 22 onto the recording layer R of the optical disc D. The objective lens 7 is a plastic single lens made in accordance with the Blu-ray Disc standard, and thus has a numerical aperture (NA) of 0.85.

  FIG. 3 is a perspective view of the objective lens actuator 10. In FIG. 3, an arrow z indicates a direction parallel to the optical axis of the objective lens 7 (that is, a direction perpendicular to the optical disk D clamped on the spindle 3, hereinafter referred to as “focusing direction”), and an arrow x indicates the spindle. 3 shows the radial direction of the disc D clamped (hereinafter referred to as “track row direction”), and the arrow y is tangential to the pit row of each track on the recording surface R of the disc D, that is, orthogonal to the track row direction. Direction (hereinafter referred to as “pit row direction”).

  As shown in FIG. 3, the objective lens actuator 10 has a substantially prismatic shape with the minor axis direction in the track row direction and is fixed to the inside of the carriage 4, and the track row. It has a substantially prismatic shape with the long-axis direction in the direction and substantially the same length as the wire fixing mount 11 and is supported by the wire fixing mount 11 so as to be swingable via 4 × 2 wires W. A lens holder 12 having a through-hole (not shown) into which the objective lens 7 is fitted in the center thereof, and a pair of focus magnets 18 fixed to the center of each side surface of the lens holder 12 facing the pit row direction, 18 and fixed to both sides of the focus magnets (permanent magnets) 18 and 18 on the respective side surfaces (on both sides in the track row direction). Four tracking magnets (permanent magnets) 20 and a portion equivalent to each arm of the Greek cross-shaped plate are bent to have a U-shaped cross section, and the lens holder 12 is mounted from the tray 2 side. A base 30 fixed in the carriage 4 so as to surround, and a pair of focus coils 15 and 16 fixed to face the focus magnets 18 and 18 on the inner surfaces of the portions extending in the focusing direction of the base 30, respectively. A total of four tracking coils 13, 13, 14, 14 fixed to the respective tracking magnets 20 on each side surface facing the track row direction in each portion of the base 30 extending in the focusing direction, and a lens Fixed to the four circumferences of the edge 12c of the through hole (not shown) on the upper surface of the holder 12. The four heaters 40 to 43 having a substantially rectangular parallelepiped shape (that is, the heaters (A) 40 and (C) 42 arranged in the track row direction with the objective lens 7 interposed therebetween) and the pits with the objective lens 7 interposed therebetween The heaters (B) 43 and (D) 41) are arranged in the row direction.

  Both ends of the wire fixing mount 11 are formed as ears 11a and 11a having a reduced thickness in the pit row direction in order to increase the effective length of the wire W.

  Similarly, both ends of the lens holder 12 in the track row direction are also formed as ears 12a and 12a having a reduced thickness in the pit row direction in order to increase the effective length of the wire W. Between the ears 11a, 12a of the wire fixing mount 11 and the lens holder 12 facing each other, four wires W that are axially directed in the pit row direction and arranged in the focusing direction respectively penetrate. Is fixed. As a result, the lens holder 12 can be translated in the track row direction and the focusing direction, respectively, while maintaining the posture in which the optical axis of the objective lens 7 is directed in the focusing direction. In addition, the 4 × 2 wires W in total also serve as supply lines for supplying current (heating element control signals) from the control block 30 (a control circuit 311 described later) to each of the heaters 40 to 43 individually. .

  The laser light focused on the recording layer by the objective lens 7 is reflected by the recording layer R to become modulated light according to the information recorded on the recording layer R, and diverges on the objective lens 7. Incident light is converted into parallel light by the objective lens 7 and incident on the collimating lens 22. Then, the light is converted into convergent light by the collimating lens 22, is incident on the beam splitter 9, is partially reflected, and is incident on the sensor lens (cylindrical lens) 25. The sensor lens 25 converges the incident reflected light on the light receiving element 26.

  As shown in FIG. 4, the light receiving element 26 is divided into four light receiving regions around the optical axis of the sensor lens 25 (accordingly, the optical axes of the objective lens 7 and the collimator lens 22). , D are arranged in a direction equivalent to the track row direction across the optical axis, and the other pair A, C is arranged in a direction equivalent to the pit row direction across the optical axis.

  The light receiving element 26 uses, as a reproduction signal (RF signal), a reproduction circuit (not shown) and a total sum of the amounts of light received by these four light receiving elements (sum of signals output from the respective light receiving elements) The data is output to the control block 30 (an amplifier 312 described later).

  The light receiving element 26 generates a focus error signal (FE signal) using a known astigmatism method. That is, if astigmatism is generated in the laser light emitted from the objective lens 7 as shown in FIG. 5, the phase is advanced in the plane where the phase is advanced near the beam waist (from the circular beam position). It converges at a position close to the objective lens 7 and converges later (at a position farther from the objective lens 7 than the circular beam position) in a plane whose phase is delayed. As a result, the cross-sectional shape of the laser beam is once linear (at the position of α in FIG. 5b) closer to the objective lens 7 than the circular beam position (the direction of the surface in which the phase is delayed [pit row direction, FIG. 5). In the example, after converging in the shape of a line parallel to the track row direction], it passes through an ellipse whose major axis faces the pit row direction, and is circular near the middle of both lines (position β in FIG. 5b). Then, it passes through an ellipse whose major axis is directed to the track row direction, and again at a position farther from the objective lens 7 than the beam waist (position γ in FIG. 5b) (the direction of the surface in which the phase is advanced [track In the example shown in FIG. 5, the line is parallel to the bit string direction]. The spot shape of the laser beam formed on the recording surface R (that is, the cross-sectional shape on the recording surface R) is directly affected by the astigmatism due to these elements through the objective lens 7 and the collimator lens 22 (or astigmatism). Projected on the light receiving element 26. Therefore, the difference between the sum of the amounts of light received by the pair A and C and the sum of the amounts of light received by the other pair B and D in each light receiving region constituting the light receiving element 26 ((A + C) − If (B + D)) is calculated, the signal becomes zero when the beam waist is positioned on the recording surface R. The light receiving element 26 converts this signal into a focus error signal (as shown in FIG. 7, “zero” at a position where the beam waist coincides with the recording surface R, and the beam waist is closer to the objective lens 7 than the recording surface R). The signal is input to the control block 30 (a later-described amplifier 317) as an FE signal indicating an FE value having a positive polarity at a certain time and a negative polarity at a far side.

  The light receiving element 26 generates a tracking error (TE signal) using a known push-pull method. That is, the difference between the amounts of light received by the pair of light receiving regions B and D arranged in the track row direction is calculated as a tracking error signal (TE signal) and input to the control block 30 (amplifier 313 described later).

  Next, the control block 30 controls the spindle 3 to rotate the disk D, controls the tracking motor 27 to move the carriage 4 in the track row direction, and controls various control signals (laser light source 8) to the optical pickup. The tracking servo (the tracking motor 27 is controlled and the tracking error correction signal is input to the objective lens actuator 10, and the tracking error is input by inputting the drive signal for, the focusing signal and the tracking error correction signal for the objective lens actuator 10. Is adjusted to make the pit row of each track follow the irradiation of the laser beam and focus servo (by inputting a focusing signal to the objective lens actuator 10, the disk D is While performing that holds the relative position of the objective lens 7 constant) to, and reads data from the recording surface R of the disc D. During this time, the control block 30 detects the state of aberration of the laser light emitted from the objective lens 7 and inputs a heating element control signal to the objective lens actuator 10 in accordance with the state of the aberration, thereby generating heat described later. The body is selectively heated to correct the aberration.

  Specifically, the control block 30 has a circuit configuration partially shown in FIG. In other words, this control block has the RF signal amplitudes to which the output signals of the amplifiers 312, 313, 317, and the amplifiers 312 and 317 for amplifying the RF signal, TE signal, and FE signal output from the light receiving element 26 are respectively input. The maximum FE value detection calculation circuit 314, and the output signals of the amplifiers 313 and 317 are inputted respectively. The TE signal amplitude maximum FE value detection calculation circuit 315, and the difference between the output signals of both the calculation circuits 314 and 315 is calculated. The differential amplifier 316 and the amplifier 317 output signals and FE value difference signals that are output as FE value differences are input, and the spindle 3, tracking motor 27 control signal, pickup control signal, and heating element control signal described above are output. The control circuit 311 is configured.

  Among these, the RF signal amplitude maximum FE value detection circuit 314 cooperates with the control circuit 311 to indicate the value of the FE signal corresponding to the position of the objective lens 7 where the amplitude of the RF signal is maximum. "FE value at maximum amplitude" is output. That is, in order to obtain the “FE value at the maximum RF signal amplitude”, the control circuit 311 uses the tracking servo function and the focus servo function described above to perform the focusing signal and tracking error for the objective lens actuator 10 described above. While appropriately outputting a correction signal and a control signal for the tracking motor 27, the laser light is emitted from the laser light source 8, and the disk D is rotated by the spindle 3. Further, by controlling the objective lens actuator 10, the objective lens 7 is moved from a position close to the disk D so that the FE signal output from the light receiving element 26 changes from a predetermined lower limit value to a predetermined upper limit value. Move relative to the direction of separation. In the meantime, the received RF signal (a high value is obtained when the pits on the recording surface R are irradiated with laser light, and a low value is obtained when the laser light is irradiated on portions other than the pits. The amplitude of the signal oscillating at a constant period is monitored, and the value of the FE signal when the maximum amplitude is reached is clamped as the “FE value at the maximum RF signal amplitude” and input to the differential amplifier 316. .

  On the other hand, the TE signal amplitude maximum FE value detection circuit 315 cooperates with the control circuit 311 to indicate the value of the FE signal corresponding to the position of the objective lens 7 at which the TE signal amplitude is maximum. "Hour FE value" is output. That is, in order to obtain the “FE value at the maximum TE signal amplitude”, the control circuit 311 appropriately outputs a focusing signal for the objective lens actuator 10 using a known focus servo function, and a laser light source. The laser beam is emitted from 8 and a control signal for the tracking motor 27 is output as appropriate, so that the jump of the laser beam irradiation target track is repeated at high speed between adjacent tracks. Further, by controlling the objective lens actuator 10, the objective lens 7 is moved from a position close to the disk D so that the FE signal output from the light receiving element 26 changes from a predetermined lower limit value to a predetermined upper limit value. Move relative to the direction of separation. In the meantime, the received TE signal (a high value is obtained when the laser beam is irradiated onto the track [pit row] on the recording surface R, and a low value is obtained when the laser beam is irradiated between the tracks. The amplitude of the signal oscillates at a constant period with a jump) is monitored, and the value of the EF signal when the maximum amplitude is reached is clamped as the “FE value at the maximum TE signal amplitude” and the differential amplifier 316 is clamped. Enter it.

  The differential amplifier 316 calculates the difference between the input FE value when the RF signal amplitude is maximum and the FE value when the TE signal amplitude is maximum (FE value when the RF signal amplitude is maximum−FE value when the TE signal amplitude is maximum) to obtain the FE value. The difference signal is input to the control circuit 311. The significance of this FE value difference signal will be described with reference to FIGS. As described above with reference to FIG. 5, in the case where the light beam emitted from the objective lens 7 has astigmatism, the laser light is separated in two orthogonal cut surfaces (spherical cut surface and meridian cut surface). Therefore, after converging in an elliptical shape, a circular spot is formed (β) and further converged in an elliptical shape in the orthogonal direction (γ). In the example of FIG. 5, since the direction of the straight line where the laser beam first converges coincides with the track row direction, the objective lens 7 is brought close to the disk D as shown in order in FIGS. When gradually moving away from the position, the elliptical laser beam having the major axis in the track row direction is projected onto the recording surface R (a), and then a circular spot is projected onto the recording surface R. (B) Finally, an elliptical laser beam having a major axis in the pit row direction is projected onto the recording surface R (c). In the state (a), since the laser beam is most converged in the pit row direction, the contrast between the reflected light on the pit and the reflected light between the pits is the strongest, and therefore the RF signal amplitude Is the maximum. On the other hand, since the laser light remains diverging in the track row direction, the contrast between the reflected light on the track and the reflected light between the tracks is weak, and therefore the TE signal amplitude is small. On the other hand, in the state (c), since the laser beam is diverging in the pit row direction, the contrast between the reflected light on the pit and the reflected light between the pits is weakened, and therefore the RF signal amplitude is also small. Become. On the other hand, since the laser beam is most converged in the track row direction, the contrast between the reflected light on the track and the reflected light between the tracks is the strongest, and thus the TE signal amplitude is maximized. .

  FIG. 8 shows the correlation between the lens position (that is, the FE value) described above, the RF signal amplitude, and the TE signal amplitude. In FIG. 8, the horizontal axis indicates the lens position (that is, the FE value difference), and the vertical axis indicates the values of the RF signal amplitude and the TE signal amplitude. As described above, when astigmatism is generated in the laser light, the FE value (a) at the maximum RF signal amplitude and the FE value (c) at the maximum TE signal amplitude are shifted, and the shift amount between the two. (FE value difference) indicates the amount of astigmatism.

  In the example shown above, the direction in which astigmatism occurs (that is, the direction in which the phase delay occurs and the direction in which the advance occurs) coincides with the pit row direction and the track row direction, respectively. Although the absolute value of the maximum value of each amplitude is the maximum, even if these directions are deviated, the absolute amount is lower than that, but the peak of each amplitude occurs at a different position. There is no problem in detecting the amount of astigmatism. In any case, this method can detect the astigmatism (component) in the track row pit row direction, and the astigmatism in the track row direction and the pit row direction contributes to the deterioration of the detection signal. By performing control according to the detected astigmatism, this signal degradation can be minimized. As described above, the beam cross section of the laser beam converged by the objective lens by the light receiving element 26, the FE value detection circuit 314 at the maximum RF signal amplitude, the FE value detection circuit 315 at the maximum TE signal amplitude, the differential amplifier 316, and the control circuit 311. This corresponds to phase detection means for detecting the distribution of the phase in the inside.

  FIG. 9 shows a state in which no astigmatism has occurred in the laser beam that is the target of control by the control circuit 311. In this case, the beam shape of the laser beam is a perfect circle across the beam waist. Therefore, as shown in FIG. 10, which is a graph having the same dimensions as FIG. 8, both the RF signal amplitude and the TE signal amplitude are maximized at the position where the beam waist is projected onto the recording surface R (FE value). Therefore, in this case, the FE value difference is “zero” indicating that there is no astigmatism.

  Therefore, the control circuit 311 individually supplies current (heating element control signal) to four heaters 40 to 43, which will be described later, as current control means, thereby individually heating the heaters 40 to 43. Therefore, a specific astigmatism that cancels the astigmatism generated in the laser beam is generated in the objective lens itself, and as a result, the astigmatism of the laser beam irradiated to the recording surface R becomes zero. Is trying to create.

  Specifically, when the polarity of the FE value difference indicated by the input FE value difference signal is − (that is, the position where the RF signal amplitude becomes maximum when viewed from the objective lens 7 is the control circuit 311, the TE signal amplitude is Is closer to the objective lens than the maximum position, that is, in the state shown in FIGS. 5, 7, and 8), a pair of heaters (B) 43 and (D) 41 arranged in the pit row direction. In addition, a current (heating element control signal) is supplied. At that time, if the current (heating element control signal) is already supplied to the pair of heaters (A) 40 and (C) 42 arranged in the track direction, the current supply amount is reduced. As a result, only the diameter direction along the pit row direction in the objective lens 7 is heated more than other portions, the refractive index of the medium in that portion is lowered, and the cross section along the pit row direction in the objective lens 7 itself. Only, there is a decrease in refractive power, and hence a phase delay. That is, astigmatism occurs in the objective lens 7 itself. FIG. 11 shows a current that gradually increases from 0 [mA] only to the heaters (B) 43 and (D) 41 when the objective lens 7 is in an environment of room temperature (25 degrees Celsius). Is a graph obtained by plotting the direction and amount [λrms] (corresponding to the FE value difference) of astigmatism generated in the objective lens 7 as the temperature of the objective lens 7 increases. This graph shows a tendency that the value of astigmatism generated in the objective lens 7 itself increases toward the + side as the current value [mA] supplied to the heaters 41 and 43 increases. . As a result, astigmatism generated in the laser beam due to various errors is canceled out with astigmatism generated in the objective lens 7 itself.

  On the other hand, when the polarity of the FE value difference indicated by the input FE value difference signal is + (that is, the position where the RF signal amplitude is maximum when viewed from the objective lens 7 is the position where the TE signal amplitude is maximum). Current (heating element control signal) is supplied to the pair of heaters (A) 40 and (C) 42 arranged in the track row direction. At that time, if the current (heating element control signal) is already supplied to the pair of heaters (A) 40 and (C) 42 arranged in the track row direction, the current supply amount is reduced. Thereby, only the diameter direction along the track row direction in the objective lens 7 is heated more than the other portions, the refractive index of the medium in that portion is lowered, and the cross section along the track row direction in the objective lens 7 itself. Only, there is a decrease in refractive power, and hence a phase delay. FIG. 12 shows that the current increases so as to gradually increase from 0 [mA] only to the heaters (A) 40 and (C) 42 when the objective lens 7 is in an environment of room temperature (25 degrees Celsius). Is a graph obtained by plotting the direction and amount [λrms] (corresponding to the FE value difference) of astigmatism generated in the objective lens 7 as the temperature of the objective lens 7 increases. This graph shows a tendency that the value of astigmatism generated in the objective lens 7 itself increases toward the minus side as the current value [mA] supplied to the heaters 40 and 42 increases. . As a result, astigmatism generated in the laser beam due to various errors is canceled out with astigmatism generated in the objective lens 7 itself.

As described above, the control circuit 311 can finally converge to the state of FIG. 9 by repeating a series of processes including the detection of the FE value difference and the adjustment of the current supply amount to the heaters 40 to 43. It is.
(Modification)
In the present invention, the plurality of heaters 40 to 43 arranged around the objective lens 7 are selectively heated to generate aberrations in the objective lens 7 itself, and thus are generated in the laser beam due to various errors. This cancels out aberrations. Accordingly, it is possible to detect the type, direction, and amount of the aberration occurring in the laser beam, and to cancel the aberration by partially heating the objective lens 7, the aberration having the reverse characteristic is the objective lens 7 itself. The present invention can be applied to correct other aberrations as long as they can be generated. For example, coma aberration can be detected by the method disclosed in Japanese Patent Laid-Open No. 2002-025091, and its phase is as shown in FIG. FIG. 2B shows the phase distribution in the cross section along the line A-W in FIG. As shown in FIG. 13, when viewed macroscopically, coma aberration is an aberration in which the phase is advanced only in one direction (a direction) at a certain diameter and the phase is delayed in the other direction (c direction) (strictly). In other words, this is an aberration of a phase distribution that draws a cubic curve having a wavefront passing through the origin and having two inflection points. Accordingly, it is possible to cancel out aberrations by advancing the phase at each of the points a, c, and d in FIG.

  For this purpose, the control circuit 311 does not supply a current (heating element control signal) to the heater in the same direction as the direction (c) in which the phase is delayed, and the direction opposite to the direction (c). A current is supplied to the heater in (a), and half of the current is supplied to the other two heaters as compared to the current supplied to the heater in the direction (a). For example, when the heater (C) 42 is in the direction (c), no current is supplied to the heater (C) 42, but the heater (A) in the opposite direction (a) is not supplied. ) Is supplied with a predetermined amount of current, and the other two heaters (B) 43 and (D) 41 are each supplied with half the predetermined amount of current.

  FIG. 14 shows that when the objective lens 7 is in an environment of room temperature (25 degrees Celsius), a current is supplied to the heater (A) 40 so as to gradually increase from 0 [mA], and the heater ( B) When the half current is supplied to 43 and (D) 41, the direction and amount of coma aberration generated in the track row direction in the objective lens 7 as the temperature of the objective lens 7 increases [ [lambda] rms] (corresponding to FE value difference). This graph shows that the coma aberration value generated in the track row direction in the objective lens 7 tends to increase toward the minus side as the current value [mA] supplied to the heaters 40, 41, and 43 increases. Show.

  FIG. 15 shows that heating is performed by supplying current to the heater (D) 41 so as to gradually increase from 0 [mA] when the objective lens 7 is in an environment of room temperature (25 ° C.). When half the current is supplied to the heaters (A) 40 and (C) 42, the coma aberration direction generated in the pit row direction in the objective lens 7 as the temperature of the objective lens 7 rises and It is a graph formed by plotting quantity [λrms] (corresponding to FE value difference). This graph shows that the coma aberration value generated in the pit row direction in the objective lens 7 tends to increase toward the minus side as the current value [mA] supplied to the heaters 40, 41, and 42 increases. Show.

  As a result, coma generated in the laser beam due to various errors is canceled with coma generated in the objective lens 7 itself.

1 is an overall perspective view of an optical disk drive device according to Embodiment 1 of the present invention. The figure which shows the optical structure of the optical component which comprises an optical pick-up, and a circuit block 2 is a perspective view of the optical pickup of FIG. The figure which shows arrangement | positioning of the light reception area | region which comprises a light receiving element Diagram showing astigmatism conceptually Block diagram showing a part of the circuit configuration of the control block Illustration of FE value Graph showing correlation between FE value, RF signal amplitude and TE signal amplitude A diagram conceptually showing the case of zero astigmatism Graph showing correlation between FE value, RF signal amplitude and TE signal amplitude when astigmatism is zero Graph showing the correlation between the current supplied to the heater and astigmatism Graph showing the correlation between the current supplied to the heater and astigmatism Diagram showing coma aberration conceptually Graph showing the correlation between the current supplied to the heater and coma Graph showing the correlation between the current supplied to the heater and coma

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 Objective lens 8 Laser light source 9 Beam splitter 10 Objective lens actuator 40-43 Heater 25 Sensor lens 26 Light receiving element 30 Control block 311 Control circuit 314 FE signal detection calculation circuit 315 at the maximum RF signal amplitude FE signal detection at the maximum TE signal amplitude Arithmetic circuit 316 Differential amplifier

Claims (2)

An optical pickup that irradiates a recording surface of an optical disc with laser light emitted from a laser light source,
An objective lens that converges laser light emitted from the laser light source onto the recording surface of the optical disc;
A pair of heaters arranged side by side in the track row direction of the optical disk and the pit of the optical disk sandwiched between the objective lens and the objective lens to heat the objective lens by heating when supplied with an electric current A pair of heaters arranged side by side in the row direction ;
Provided between the laser light source and the objective lens, and guides the laser light emitted from the laser light source toward the objective lens, and reflects off the recording surface of the optical disc and passes through the objective lens. A beam splitter for separating the reflected light of the laser light from the optical path of the laser light emitted from the laser light source;
Centered on the optical axis of the objective lens, a pair of light receiving regions are arranged in a direction equivalent to the track row direction with the optical axis in between, and another pair of light receiving regions are in the pit row direction with the optical axis in between. Generating a tracking error signal, a focus error signal, and a reproduction signal based on a light receiving element having four light receiving areas divided so as to be arranged in an equivalent direction, and a light receiving amount detected in each light receiving area in the light receiving element; Control for detecting the distribution of the phase as a difference between the value of the focus error signal when the amplitude of the tracking error signal is maximum and the value of the focus error signal when the amplitude of the reproduction signal is maximum and a circuit, wherein by receiving the separated the reflected light by the beam splitter, the converged by the objective lens A phase detection means for detecting a phase distribution in laser light beam in the cross section,
Selectively supplying current supply before Symbol current to heater disposed in the same direction as the direction that is detected that is progressing phase than other directions by said phase detecting means to said objective lens An optical pickup comprising a circuit. A spindle for rotating the optical disc, an actuator for moving the objective lens along the optical axis, and a tracking motor for moving the lens in the tracking direction;
The control circuit includes:
The spindle can be controlled, the actuator can be controlled, the tracking motor can be controlled,
A pair of light receiving regions of the light receiving elements arranged in the same direction as the track row direction of the optical disc while the target track of the laser light is alternately jumped between adjacent tracks on the optical disc by controlling the tracking motor The difference between the output signals is the tracking error signal,
While rotating the optical disc by controlling the spindle, the output signal of the light receiving element is used as the reproduction signal,
While the objective lens is advanced and retracted in the optical axis direction by controlling the actuator, a sum of output signals of a pair of light receiving regions arranged in the same direction as the track row direction and a pair of rows arranged in the same direction as the pit row direction The optical pickup according to claim 1 , wherein a difference from a sum of output signals of light receiving elements is handled as the focus error signal .