Optical Pick-up device

[0025] The embodiments of the present invention will be described in detail below with reference to the drawings.

[0026] figure 2 An overview of the optical system of the optical pickup device based on the present invention is shown. The optical pickup device has a semiconductor laser device 111 for emitting laser beams of two different wavelengths. The semiconductor laser device 111 independently emits a first laser beam with a wavelength of 650 nm and a second laser beam with a wavelength of 780 nm from different light emitting points in the same emission direction. The interval L between the light emitting points is about 100 μm.

[0027] The optical pickup device is configured so that the laser beam emitted from the semiconductor laser device 111 sequentially passes through the collimator lens 112 and the objective lens 113 and reaches the optical disc 114. DVD and CD (including CD-R) are used as the optical disc 114, and one of the used optical discs is placed on a turntable not shown.

[0028] The semiconductor laser device 111 is driven by the laser drive circuit 115. The laser driving circuit 115 drives the semiconductor laser device 111 to selectively emit the first laser beam or the second laser beam according to the type of the optical disc 14 from which information is read. Specifically, the laser driving circuit 115 drives the semiconductor laser device 111 so that the semiconductor laser device 111 emits a first laser beam with a wavelength of 650 nm when the optical disc 114 is a DVD, and makes the semiconductor laser device 111 emit a wavelength of 650 nm when the optical disc 114 is a CD 780nm second laser beam.

[0029] The lens driving mechanism 116 can move the objective lens 113 in the tracking direction 118, that is, in the radial direction of the optical disc. The lens driving mechanism 116 can be used as a known lens actuator mechanism to perform focus and tracking servo adjustments. The lens driving circuit 117 is connected to the lens driving mechanism 116. The lens drive circuit 117 generates a lens movement instruction according to the type of the optical disc 114 from which information is read, and the lens drive mechanism 116 moves the objective lens 113 by responding to the lens movement instruction.

[0030] When the optical disc 114 is a DVD, the semiconductor laser device 111 emits a first laser beam with a wavelength of 650 nm. The objective lens 113 is moved to the first position so that the center of the first laser beam is substantially aligned with the optical axis (central axis) of the objective lens 113. On the other hand, when the optical disc 114 is a CD, the semiconductor laser device 111 emits a second laser beam having a wavelength of 780 nm. The objective lens 113 is moved to the second position so that the center of the second laser beam is substantially aligned with the optical axis of the objective lens 113.

[0031] The intensity distribution of the laser beam emitted by the semiconductor laser device 111 is Gaussian. In the Gaussian distribution, such as image 3 As shown, the intensity I of the laser beam is the largest at the center of the laser beam and decreases with the distance r from the center. When the first laser beam or the second laser beam is emitted, the center of the laser beam can be substantially aligned with the optical axis of the objective lens 113 by moving the objective lens 113 described above. Therefore, whether it is a DVD or a CD, the intensity of the laser beam irradiated to the recording surface 114a of the optical disc 114 can be effectively used.

[0032] The tracking servo adjustment and focus servo adjustment when reading information from the optical disc 114 are performed with reference to the first position of the objective lens 113 when the optical disc 114 is a DVD, and are performed with reference to the second position of the objective lens 113 when the optical disc 114 is a CD.

[0033] Next, the present invention will be described more specifically. Figure 4 Shown is the general configuration of an optical disc player suitable for the present invention.

[0034] in Figure 4 In the optical disc player shown, the types of optical disc 1 that can be played include CD, CD-R, and DVD. Here, CD-R is regarded as equivalent to CD.

[0035] Such as Figure 5 with 6 As shown, the pickup device 2 has a semiconductor laser device 21 for emitting a first laser beam having a wavelength of 650 nm and a second laser beam having a wavelength of 780 nm. In addition, in this optical pickup device, the laser beam emitted by the semiconductor laser device 21 reaches the half mirror (spectroscope) 23 through the grating 22. The grating 22 is used to divide the laser beam into multiple light fluxes (Othorder light, ±primary light). Class 0 light is used for focus servo control, and ± primary light is used for tracking servo control. The half mirror 23 basically reflects the laser beam at an angle of 90° to the incident light. The direction of the reflected laser beam is in the direction of the optical disc 1. A collimator lens 24 and an objective lens 25 are placed between the half mirror 23 and the optical disc 1.

[0036] The collimator lens 24 collimates the laser beam from the half mirror 23 and supplies the collimated laser beam to the objective lens 25. The objective lens 25 is a bifocal lens, which focuses the collimated laser beam onto the recording surface 1a of the optical disc 1. The laser beam reflected by the recording surface 1 a of the optical disc 1 passing through the objective lens 25 is collimated by the collimator lens 24 and passes through the half mirror 23 in a straight line. These elements are assembled in the above order in the optical axis direction passing through the half mirror 23, the cylindrical lens 28, and the photodetector 26. The cylindrical lens 28 is an astigmatism generating element for generating astigmatism.

[0037] Figure 5 This shows a case where a DVD is used as the optical disc 1, in which the semiconductor laser device 21 emits a first laser beam with a wavelength of 650 nm. Figure 6 This represents a case where a CD (including CD-R) is used as the optical disc 1, in which the semiconductor laser device 21 emits a second laser beam with a wavelength of 780 nm.

[0038] Figure 7 Shown is a cross section of the chip of the semiconductor laser device 21. Such as Figure 7 As shown, the semiconductor laser device 21 is formed on one chip, and a single n-type GaAs substrate 30 having a separation groove 33 between two emitters has a first light emitter 31 and a second light emitter on one main surface. A transmitter 32, wherein the first light transmitter 31 has a first light emission point A1 for emitting a first laser beam with a wavelength of 650 nm, and the second light transmitter 32 has a second laser beam for emitting a second laser beam with a wavelength of 780 nm The second light emission point A2. The first light emitter 31 and the second light emitter 32 are in a layered structure described below. Furthermore, the semiconductor laser device 21 has a back electrode 34 on the other main surface of the substrate 30, which is a common electrode of the two light emitters 31, 32. The light emitting surface of the first light emitter 31 having the light emitting point A1 and the light emitting surface of the second light emitter 32 having the light emitting point A2 are positioned in the same emitting direction.

[0039] The first light emitter 31 has an n-type AlGaInP cladding layer 41, a distortion quantum well active layer 42, a p-type AlGaInP cladding layer 43, and an n-type GaAs layer 44 in order starting from the GaAs substrate 30. , P-type GaAs layer 45 and electrode 46. The cross section of the cladding layer 43 is formed so that the center part thereof is trapezoidal. The n-type GaAs layer 44 is formed to cover the cladding layer 43 except for the upper surface of the trapezoid. The p-type GaInP layer 47 is formed on the upper surface of the trapezoid. The first light emission point A1 is located in the distortion variable sub-well active layer 42.

[0040] The second light emitter 32 is in a so-called double heterodyne structure, and has a pair of n-type AlGaAs buried layers 51, 52 on the GaAs substrate 30 with a predetermined interval therebetween. An electrode 55 is provided on each buried layer of the pair of n-type AlGaAs buried layers 51, 52 through insulating layers 53, 54. On the GaAs substrate 30 between the buried layers 51 and 52, an n-type AlGaAs cladding layer 56, an undoped GaAs active layer 57, and a p-type AlGaAs cladding layer 58 are sequentially stacked. The clad layer 58 is in contact with the electrode 55. The second light emission point A2 is located in the active layer 57. The interval between the optical axis of the first light emission point A1 and the optical axis of the second light emission point A2 is, for example, 100 μm.

[0041] Such as Figure 5 with 6 As shown, the semiconductor laser devices 21 are fixed on the insulator fixing member, and they are also covered with a housing part 21a.

[0042] The light detector 26 has Figure 8 Three independent light receiving elements 71-73 are shown. The light receiving surfaces of the light receiving elements 71-73 are located on a plane perpendicular to the optical axis, and all are rectangular. Furthermore, the light receiving elements 71-73 are arranged in a line in their longitudinal direction. The light-receiving element 71 is located between the light-receiving elements 72 and 73, and receives the 0th order light formed by the grating 22. The light receiving element 71 has its light receiving surface divided into eight, and is composed of eight light receiving elements 71a-71h. Specifically, the light receiving surface of the light receiving element 71 is divided into eight parts by a longitudinal bisecting line and a quadrant perpendicular to the bisecting line. An output signal corresponding to the intensity of the received light on the light receiving surface is generated by each of the eight light receiving elements 71 a to 71 h of the light receiving element 71. In each of the light receiving elements 72, 73, the light receiving surface is not divided, and the output signal is generated corresponding to the received light intensity on the light receiving surface. The light receiving element 72 receives one of the reflected light of ± primary light formed by the grating 22, and the light receiving element 73 receives the other reflected light of ± primary light. in Figure 8 Here, the dashed-dotted line is a center line shared by the respective light receiving surfaces of the light receiving elements 71 to 73.

[0043] Such as Figure 4 As shown, the first light emitter 31 of the semiconductor laser device 21 is driven by a driver 67, and the second light emitter 32 is driven by a driver 68. The system control circuit 6 is connected to the drivers 67 and 68. The system control circuit 6 provides driving instructions to one of the drives 67 and 68 for playing the optical disc 1 according to the type of the optical disc 1. The operation of discriminating the type of the optical disc 1 will be described later.

[0044] The pickup device 2 is also equipped with a tracking actuator (not shown) for moving the position of the beam spot in the radial direction of the optical disc, and a focusing actuator (not shown) for adjusting the focal position of the beam spot.

[0045] The output signals of the light receiving elements 71-73 are supplied to the preamplifier 3 and the error generator circuit 4. As described below, the preamplifier 3 generates an RF signal based on the output signal of the light receiving element 71, and amplifies the signal to be supplied to the information data reproduction circuit 27 as the RF signal Rf.

[0046] After digitizing the output RF signal Rf of the preamplifier 3, the information data reproduction circuit 27 performs demodulation and error correction processing to recover the data recorded on the optical disc 1. Also, the information data reproduction circuit 27 performs information (video, audio, computer data) demodulation processing on the restored data to reproduce the information data output as the reproduction information data.

[0047] Such as Picture 9 As shown, the error generator circuit 4 has a focus error signal generator circuit 84 and a tracking error signal generator circuit 85. The focus error signal generator circuit 84 generates a focus error signal FE according to each output signal of the light receiving element 71 to indicate the focus error of the beam spot on the recording surface 1a of the optical disc 1, and the tracking error signal generator circuit 85 according to the light The respective output signals of the receiving elements 72 and 73 generate a tracking error signal TE, which is used to indicate the error of the beam spot on the optical disc 1 relative to the center of the track in the optical disc radial direction. These error signals are provided to the servo control circuit 5. In addition, the error generator circuit 4 also supplies the tracking error signal TE to the track cross signal generator circuit 86.

[0048] The track cross signal generator circuit 86 generates a binary track cross signal TZC and provides this signal to the system control circuit 6. When the signal level of the tracking error signal TE generated during the track jump of the pickup device 2 is higher than At a predetermined level, the signal TZC is at a logic level "1", and when it is lower than a predetermined level, it is at a logic level "0". In other words, every time the pickup device 2 traverses the recording track on the optical disc 1 during the track jump, the track crossing signal generator circuit 86 outputs the track crossing signal TZC to switch the logic level to such as "0", "1" "And "0". The track cross signal TZC is supplied to the system control circuit 6.

[0049] Such as Picture 9 As shown, in the servo control circuit 5, the rotation speed detector 79 is supplied with a frequency signal FG, which is an AC signal indicating the current rotation frequency of the spindle motor 11 that rotates the optical disc 1 by the turntable. The rotation speed detector 79 generates a rotation speed signal to indicate the rotation speed of the main shaft corresponding to the frequency signal FG, and the rotation speed signal is provided to the rotation speed error generator 80. The rotation speed error generator 80 generates a rotation speed error signal to indicate the difference between the rotation speed signal and the reference rotation speed signal provided by the system control circuit 6, and provides the rotation error signal to the equalizer 81. The equalizer 81 generates the spindle drive signal SPD through the rotation speed error signal, and the spindle drive signal SPD is supplied to the spindle motor 11 through the driver 10 when the switch 82 is turned on. The spindle motor 11 drives the optical disc 1 to rotate at a rotation speed according to the spindle drive signal SPD. The AC generator (not shown) equipped with the spindle motor 11 provides the servo control circuit 5 with a frequency signal FG corresponding to the rotation frequency of the current time. The spindle servo system can be used to drive the spindle motor 11 to rotate at the rotation speed indicated by the reference rotation speed signal provided by the system control circuit 6.

[0050] In addition, in the servo control circuit 5, the focus error signal FE is supplied to the equalizer 74, and the focus drive signal FD is generated by the equalizer 74 and supplied to the driver 9 when the switch 75 is turned on. The driver 9 drives the focus actuator equipped in the pickup device 2 according to the focus drive signal FD, and the focus actuator performs an operation to adjust the focus position of the beam spot irradiated to the optical disc 1.

[0051] Also, in the servo control circuit 5, the tracking error signal TE is supplied to the equalizer 76, and the tracking drive signal TD is generated by the equalizer 76 and supplied to the driver 9 through the adder 20 when the switch 77 is turned on. The driver 9 drives the tracking actuator provided in the pickup device 2 according to the tracking drive signal TD, and the tracking actuator moves the position of the beam spot irradiated to the optical disc 1 to a position corresponding to the drive current through the tracking drive signal TD. section.

[0052] Each switch 75, 77, 82 is turned on/off in response to an instruction from the system control circuit 6. The switch 75 is turned on during the focus servo control; the switch 77 is turned on during the tracking servo control; and the switch 82 is turned on during the spindle servo control.

[0053] And even though Picture 9 Not shown in, but the servo control circuit 5 also generates a sliding contact drive signal SD according to the tracking error signal TE and provides this signal to the sliding contact 100 through the driver 8. In this way, the sliding contact 100 moves the pickup device 2 in the radial direction of the optical disc by the sliding contact driving signal SD at a rotation speed corresponding to the driving current.

[0054] The system control circuit 6 including a microcomputer controls the entire optical disc player, and generates various control signals according to the operation input by the user through a manipulation unit (not shown) and the current operating state of the optical disc player. The servo control circuit 5 performs servo control operations according to various control signals generated by the system control circuit 6.

[0055] In the foregoing configuration, the first laser beam or the second laser beam emitted by the semiconductor laser device 21 is divided into a plurality of light fluxes (0-order light, ±primary light) by the aforementioned grating 22, and then reflected by the half mirror 23. The laser beam reflected by the half mirror 23 is collimated by the collimator lens 24 and reaches the objective lens 25. The laser beam is condensed on the recording surface 1a of the optical disc 1 by the objective lens 25 to form an elliptical spot.

[0056] The light beam reflected and modulated by the information pits of the recording surface 1a of the optical disc 1 returns to the half mirror 23 through the objective lens 25 and the collimator lens 24 and is separated from the optical path from the semiconductor laser device 21 here, and is incident through the cylindrical lens 28 To the respective light receiving elements 71-73 of the light detector 26. The reflected light of the 0th order light from the optical disc 1 reaches the light receiving element 71, and the reflected light of the ±primary light from the optical disc 1 reaches the light receiving elements 72, 73.

[0057] When the first laser beam with a wavelength of 650 nm is emitted from the first light emitter 21 and the elliptical light spot formed by the first laser beam on the recording surface 1a of the optical disc 1 is located on the focused track, such as Picture 10 As shown, circular light spots 61-63 are formed on the respective light-receiving surfaces of the light-receiving elements 71-73 of the photodetector 26. On the light-receiving element 71, a circular spot 61 of zero-order light is formed in the center of the dividing intersection point on the light-receiving surfaces of the light-receiving elements 71a, 71b, 71e, 71f, and on the light-receiving elements 72, 73, The circular light spots 62, 63 of the ± primary light are formed at positions having a predetermined distance interval from the light spot 61 of the 0-order light. In other words, on the light receiving surface of the light receiving element 72, the light spot 62 is located on the side away from the light receiving element 71 away from the longitudinal center, and on the light receiving surface of the light receiving element 73, the light spot 63 is located off the longitudinal center. The side close to the light receiving element 71. Also, in the relationship where the dividing line directions of the light receiving surfaces of the light receiving elements 71a, 71e and the light receiving surfaces of 71b, 71f are aligned with the track direction of the optical disc 1, light spots are formed on the light receiving surfaces.

[0058] When the second laser beam with a wavelength of 780 nm is emitted from the second light emitter 22 and the elliptical light spot formed by the second laser beam on the recording surface 1a of the optical disc 1 is located on the focused track, such as Picture 11 As shown, circular light spots are formed on the light receiving surfaces of the light receiving elements 71 to 73 of the light detector 26, respectively. In the light-receiving element 71, a circular spot 61 of zero-order light is formed in the center of the division intersection points on the light-receiving surfaces of the light-receiving elements 71c, 71d, 71g, 71h, and on the light-receiving elements 72, 73, Circular light spots 65, 66 of ± primary light are formed at positions having a predetermined distance interval from the light spot on the light receiving element 71. In other words, on the light receiving surface of the light receiving element 72, the light spot is located on the side close to the light receiving element 71 away from the longitudinal center, and on the light receiving surface of the light receiving element 73, the light spot is located away from the longitudinal center. One side of the receiving element 71. Also, in the relationship where the dividing line directions of the light receiving surfaces of the light receiving elements 71c, 71g and the light receiving surfaces of 71d, 71h are aligned with the track direction of the optical disc 1, light spots are formed on the light receiving surfaces.

[0059] The RF signal Rf and the focus error signal FE are generated based on the output signals of the respective light receiving elements 71a to 71h of the photodetector 26. In addition, the tracking error signal TE is generated based on the output signals of the respective light receiving elements 72 and 73. Assuming that the output signals of the light receiving elements 71a-71h are Aa-Ah respectively, and the output signals of the light receiving elements 72 and 73 are B and C respectively, then when the first laser beam with a wavelength of 650nm is transmitted by the first transmitter 21 When transmitting, the RF signal Rf can be calculated in the preamplifier 3 as follows:

[0060] Rf=Aa+Ab+Ae+Af,

[0061] In the focus error signal generator circuit 84, the focus error signal FE is calculated as follows:

[0062] FE=(Aa+Af)-(Ab+Ae)

[0063] And in the tracking error signal generator circuit 85, the tracking error signal TE is calculated as follows:

[0064] TE=B-C.

[0065] When the second laser beam with a wavelength of 780 nm is emitted by the second transmitter 22, in the preamplifier 3, the RF signal Rf is calculated as follows:

[0066] Rf=Ac+Ad+Ag+Ah,

[0067] In the focus error signal generator circuit 84, the focus error signal FE is calculated as follows:

[0068] FE=(Ac+Ah)-(Ad+Ag)

[0069] And in the tracking error signal generator circuit 85, the tracking error signal TE is calculated as follows:

[0070] TE=B-C.

[0071] When the switch 75 is turned on, the focus error signal FE is supplied to the driver 9 as a focus drive signal FD through the equalizer 74. According to the focus drive signal FD, the driver 9 causes the focus actuator to move the objective lens 2 in the optical axis direction to adjust the focus position of the beam spot irradiated to the optical disc 1.

[0072] When the switch 77 is turned on, the tracking error signal TE is supplied to the driver 9 as a tracking drive signal TD through the equalizer 76. According to the tracking drive signal TD, the driver 9 causes the tracking actuator to move the objective lens 25 in the radial direction of the optical disc to adjust the position of the beam spot irradiated to the optical disc 1 in the radial direction of the optical disc.

[0073] When the optical disc 1 is placed on the turntable, the system control circuit 6 performs an optical disc type discriminating operation for discriminating the disc type.

[0074] In the disc type identification operation, such as Picture 12 As shown, the system control circuit 6 first generates a light emission driving command to the driver 67 or 68 (step S1). For example, when the driver 67 has a light emission driving command, the driver 67 provides a driving current between the electrodes 34 and 46 of the first light emitter 31 of the semiconductor laser device 21 by responding to the light emission driving command, so that the light emitter 21 The light emitting point A1 emits the first laser beam.

[0075] After performing step S1, the system control circuit 6 stops the spindle servo control, starts the focus servo control, and stops the tracking servo control (step S2). Specifically, the switch 75 is turned on and the switches 77 and 82 are turned off. Since only the focus servo control operation is performed, the focus of the beam spot of the laser beam is adjusted on the optical recording surface 1a of the optical disc 1.

[0076] The system control circuit 6 generates a forced drive command of the sliding contact servo system to the servo control circuit 5 (step S3). In response to the forced driving command, the servo control circuit 5 provides a predetermined driving pulse to the driver 8 so that the sliding contact 100 moves the pickup device 2 a predetermined distance in the radial direction of the optical disc for the jump track. Next, the number of pulses corresponding to "1" of the binary track cross signal generated by the track cross signal generator circuit 86 during the track jump period is calculated (step S4). After step S4 is executed, the calculated pulse number represents the number of tracks during the track jump period, so it is determined whether the count value is greater than a predetermined threshold (step S5). If the calculated number of pulses> a predetermined threshold, it can be determined that the optical disc 1 is a DVD. If the calculated number of pulses ≤ a predetermined threshold, it is determined that the optical disc 1 is a CD.

[0077] In order to play the optical disc 1, after the disc type discriminating operation ends, the system control circuit 6 performs an optimal position detection operation of the objective lens for adjustment by moving the objective lens 25 in the radial direction of the optical disc to provide the maximum RF signal Rf.

[0078] In the operation of detecting the best position of the objective lens, such as Figure 13 As shown, the system control circuit 6 first generates a light emission drive command based on the result of the disc type discriminating operation (step S11). When the optical disc 1 is discriminated as a DVD, the drive 67 has a light emission drive command. Therefore, by responding to the light emission driving command, the driver 67 provides a driving current between the electrodes 34, 46 of the first light emitter 31 of the semiconductor laser device 21, so that the light emission point A1 of the first light emitter 31 emits the first light. A laser beam. When the optical disc 1 is discriminated as a CD, the drive 68 has a light emission drive command. Therefore, by responding to the light emission driving command, the driver 68 provides a driving current between the electrodes 34, 56 of the second light emitter 32 of the semiconductor laser device 21, so that the light emission point A2 of the second light emitter 32 emits the second light. Two laser beams.

[0079] After step S11 is executed, the system control circuit 6 starts the spindle servo control, starts the focus servo control, and stops the tracking servo control (step S12). Specifically, the switches 75 and 82 are turned on, and the switch 77 is turned off. Since the focus servo control and spindle servo control operations are being performed, the optical disc 1 is driven to rotate, and the beam spot of the emitted laser beam is adjusted on the recording surface 1 a of the optical disc 1. Furthermore, the system control circuit 6 generates an objective lens shift instruction to the pressurizing circuit 19 in the servo control circuit 5 (step S13). In response to the objective lens shift instruction, the pressurizing circuit 19 supplies the driver 9 with a gradual driving voltage through the adder 20. In this way, the driver 9 drives the objective lens 25 through the tracking actuator to move the objective lens 25 within the movable range in the radial direction of the optical disc.

[0080] After step S13 is performed, the system control circuit 6 determines whether the objective lens 25 has moved completely within its movable range (step S14). If the objective lens 25 has not moved completely within its movable range, the maximum value of the RF signal Rf detected by the maximum value detector circuit 40 may be monitored to determine whether the maximum value of the RF signal Rf is detected (step S15). When the maximum value is detected, the driving voltage of the pressurizing circuit 19 when the maximum value is obtained is stored as VMAX in a memory not shown (step S16). Then, it returns to step S13 to continue the movement of the objective lens 25. On the other hand, when it is determined in step S14 that the objective lens has moved completely within its movable range, the objective lens best position detection operation ends. The driving voltage VMAX stored at this time is the maximum value of the actual RF signal Rf in the entire movable range of the objective lens 25.

[0081] The RF signal Rf increases or decreases with the distance between the center of the Gaussian distribution and the optical axis of the objective lens 25. Specifically, the RF signal Rf decreases as the distance increases. In addition, in addition to the distance, the RF signal Rf is different when the position of the beam spot on the optical disc is on track and when it is off track. Specifically, the RF signal Rf is larger when the beam spot position is not on the track than when it is on the track. However, since the spindle servo control operates to drive the optical disc 1 to rotate when the tracking servo control is stopped, the position of the beam spot randomly appears on the track and does not appear on the track. Therefore, during the operation of detecting the best position of the objective lens, the time average level of the RF signal Rf is hardly affected by the on-track and off-track. As a result, the distance between the center of the Gaussian distribution of the laser beam and the optical axis of the objective lens 25 can be determined by the amplitude of the RF signal Rf, and the center of the laser beam is substantially aligned with the objective lens through the objective lens optimal position detection operation here. The moving position of the objective lens 25 of the optical axis 25 can be detected as the driving voltage VMAX.

[0082] During reproduction of the optical disc 1, the system control circuit 6 selects the emitted laser beam of the semiconductor laser device 21 according to the type of the optical disc 1 obtained in the disc type discriminating operation. In addition, the pressurizing circuit 19 generates the driving voltage VMAX, the spindle servo control is activated, the focus servo control is activated, and the tracking servo control is activated. When the optical disc 1 is a DVD, the semiconductor laser device 21 emits a first laser beam with a wavelength of 650 nm. The objective lens 25 is moved to the first position corresponding to the driving voltage VMAX so that the optical axis of the objective lens 25 is substantially aligned with the center of the first laser beam. On the other hand, when the optical disc 1 is a CD, the semiconductor laser device 21 emits a second laser beam with a wavelength of 780 nm. The objective lens 25 is moved to the second position corresponding to the driving voltage VMAX so that the optical axis of the objective lens 25 is substantially aligned with the center of the second laser beam.

[0083] In the tracking servo control, the driving voltage VMAX is generated by the boosting circuit 19, and the driving voltage VMAX is added as an offset voltage in the adder 20 to the tracking driving signal TD from the equalizer 76. The addition result of the adder 20 is provided as a tracking drive signal TD to the driver 9 to drive the tracking actuator. Therefore, the tracking servo control is performed using the amount of movement of the objective lens 25 relative to the reference position in the radial direction of the optical disc by the offset voltage.

[0084] When the optical disc 1 is a DVD, the mechanical neutral point of the tracking actuator can be set at the middle of the reference position of the objective lens 25, and when the optical disc 1 is a CD, it is set at the reference position of the objective lens 25. In this way, in the case of a CD The amount of movement of the objective lens 25 in the opposite direction is basically the same as that in the case of a DVD. In addition, the mechanical neutral point of the tracking actuator coincides with the reference position of the objective lens 25 when the optical disc 1 is a DVD, and in the case of a CD, the objective lens 25 can be moved in the radial direction of the optical disc by an offset voltage. In other words, since signal detection in the pickup device is more difficult when a laser beam of a shorter wavelength is used, an offset voltage is not provided in the case of a DVD.

[0085] In the previous embodiment, the objective lens 25 actually moves in the radial direction of the optical disk to detect the position of each placed optical disk 1 when the RF signal Rf takes the maximum value. In addition, for each of the DVD and CD, the position of the objective lens can be preset, so that the objective lens can be moved to the preset position according to the discrimination result of the disc type discriminating operation, without the need to detect the RF signal Rf Maximum value. In addition, when the RF signal Rf is monitored for moving the objective lens to an optimal position, the error rate of the RF signal can be monitored to move the objective lens to a position with the smallest possible error rate.

[0086] In addition, in the foregoing embodiment, the objective lens 25 is a bifocal lens and can be used when the optical disc 1 is a DVD or a CD, and DVD and CD can also use different objective lenses from each other. In this configuration, for example, such as Figure 14 As shown, the objective lens 91 for DVD and the objective lens 92 for CD are fixed on the lens holder 93 so that the respective optical axes are parallel. The lens holder 93 is driven by an unshown driving device to move in the direction of the arrow 95. Such asFigure 14 As shown, when the optical disc 94 is a DVD, the lens holder 93 is moved so that the center of the irradiated first laser beam 96 with a wavelength of 650 nm is aligned with the optical axis of the objective lens 91 for the DVD. When the disc 94 is a CD, such as Figure 15 As shown, the lens holder 93 is moved so that the center of the irradiated second laser beam 97 having a wavelength of 780 nm is aligned with the optical axis of the objective lens 92 for CD. Since a mechanism for switching two objective lenses according to the type of optical disc is disclosed in detail in the published Japanese patent application NQ.10-112057, a detailed description thereof is omitted here.

[0087] In addition, although the foregoing embodiments have described the case where the present invention is applied to an infinite optical system using the collimator lens 24, the present invention can also be applied to a finite optical system.

[0088] In addition, although the focus servo control is performed based on the astigmatism method and the tracking servo control is performed based on the three-beam method in the previous embodiment, it is also possible to adopt existing methods without being limited by these methods. In addition, it is not necessary to use the same method to play CDs and DVDs. For example, the tracking servo control of CD can be performed according to the three-beam method, while the DVD can be performed according to the phase difference method, and so on.

[0089] Also, although the semiconductor laser device includes two light emission points of different light emission wavelengths in the foregoing embodiments, the present invention can be applied to a semiconductor laser device including three or more light emission points having light emission wavelengths different from each other. Also, the semiconductor laser device is not limited to having two integrated light emitters in the above-mentioned embodiment, but a semiconductor laser device having two independently formed light emitters may be used for emitting laser light having wavelengths different from each other. bundle.

[0090] As described above, according to the present invention, it is unnecessary to use an optical device such as a combined prism, and compared with the prior art, the optical system can be closely arranged to simplify the configuration of the optical pickup device and reduce the size. Moreover, since the objective lens is moved in the radial direction of the optical disc to one of a plurality of different positions corresponding to a position of one light emitter selected from the plurality of light emitters, even if the light emission of the laser beam of each light emitter is The dots with small intervals can also set the intensity of the laser beam irradiated to the recording surface of the optical disc under suitable conditions.