JP2011086354A - Optical head and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head which cancels an offset caused by an objective lens shift by using a light-detecting element having a light-receiving face pattern of simple composition, and also to provide an optical disk device. <P>SOLUTION: The optical head is equipped with: a light-detecting element 27, which includes a main light-receiving part 270 and a supplementary light-receiving part 271; and an optical element 6. The optical element 6 receives a return light beam from an optical disk 5 both in a diffraction area 601 and in a diffraction area 602, and subjects the beam to transmission and diffraction to generate a 0-order diffracted light beam D0 and ±one order diffracted light beams D1a, D1b. The diffraction area 601 generates the -one order diffracted light beam D1a, and the diffraction area 602 generates the +one order diffracted light beam D1b. The supplementary light-receiving part 271 is arranged in a position in which part of the light spot of the +one order diffracted light beam D1b is received. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical head and an optical disk apparatus equipped with the optical head.

  A one-beam push-pull method is widely known as a method for causing an optical head to follow an information track with a light beam emitted from a semiconductor laser and condensed on an information recording layer of an optical disk. According to this one-beam push-pull method, the light beam (returned light) reflected and diffracted by the information track of the optical disc is detected by the light receiving unit divided into two light receiving surfaces in the light detection element. A push-pull signal, that is, a tracking error signal is obtained as a difference between signals detected on the light receiving surfaces. The actuator can cause the optical beam to follow the recording track by shifting the objective lens in the radial direction of the optical disk so that the level of the push-pull signal approaches zero.

  However, in the conventional one-beam push-pull method, when the objective lens is driven by the actuator and shifted in the radial direction of the optical disc, the position of the objective lens and the position of the light detection element may be relatively shifted. At this time, since the center position of the light spot irradiated on the light receiving surface is shifted from the dividing line separating the two light receiving regions from each other, a DC offset (hereinafter simply referred to as “offset”) is superimposed on the push-pull signal. It is known.

  A technique for erasing this offset is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-63778. The optical pickup disclosed in Patent Document 1 includes a polarization hologram that separates zero-order light and ± first-order light from a return light beam reflected by an optical disk. The separated 0th-order light, + 1st-order light, and -1st-order light are respectively detected by the corresponding light receiving surfaces, and the difference between the detection signals of these + 1st-order light and -1st-order light is used as a push-pull signal. Here, even if the objective lens moves relative to the photodetecting element, the light receiving surface that detects the + 1st order light and the −1st order light has an area that is not affected by the amount of movement, so there is no offset. A push-pull signal can be obtained.

  As another method for causing a light beam to follow an information track of an optical disk, a three-beam push-pull method is also known. According to this method, the diffraction grating generates at least three light beams including zero-order light and ± first-order light from the light beam emitted from the semiconductor laser. These 0th-order light and ± 1st-order light beams are condensed by the objective lens on information tracks periodically arranged on the information recording layer of the optical disk. When the zero-order light beam (main beam) is focused at the center position of the information track, the ± first-order light beam (sub-beam) is shifted to both sides in the radial direction with respect to the irradiation position of the zero-order light. The light is condensed in a region (a region between the information track and another information track adjacent thereto). The return light beams of the 0th order light, the + 1st order light, and the −1st order light reflected and diffracted by the periodic structure of the information track are detected by the corresponding photodetectors. The main push-pull signal MPP can be generated from the detection signal of the return light beam of the 0th order light, and the sub push-pull signal SPP can be generated from the detection signal of the return light beam of the ± 1st order light. As in the case of the pull method, when the objective lens is driven by an actuator and shifts in the radial direction of the optical disk, and the position of the objective lens and the position of the light detection element are relatively shifted, the main push-pull signal MPP and the sub push Each offset is superimposed on the pull signal SPP.

  The main push-pull signal MPP and the sub push-pull signal SPP have opposite phases with respect to the direction crossing the information track, but have the same phase with respect to the objective lens shift (for example, when the signal level of the MPP increases in the positive direction). The signal level of the SPP also increases in the positive direction), so that the offset is canceled by subtracting the signal α × SPP obtained by amplifying the sub push-pull signal SPP with an appropriate gain from the main push-pull signal MPP. A push-pull signal (= MPP−α × SPP) can be obtained.

JP-A-8-63778 (paragraph 0017, FIG. 1)

  However, in the technique disclosed in Patent Document 1, it is necessary to prepare a light receiving surface pattern of the light detection element having a special configuration depending on the pattern of the polarization hologram, which increases the manufacturing cost of the optical head. There is a problem of causing it.

  On the other hand, in the 3-beam push-pull method, a general-purpose light-receiving surface pattern having a simple configuration can be adopted. However, in the information recording layer of the optical disc, when information is recorded by focusing the main beam (zero-order light beam) on a certain information track, information is not overwritten on other information tracks adjacent to the information track. Alternatively, it is necessary to sufficiently reduce the light intensity of the sub beam (± first order light beam) so as not to erase the recording information of the other information track. If the light intensity of the sub beam is too low, when the return light beam corresponding to the sub beam is received by the light detection element, the detected light amount becomes small. In this case, if the sub push-pull signal SPP is amplified in order to cancel the offset due to the objective lens shift, there is a problem that the noise component included in the sub push-pull signal SPP is greatly amplified.

  Here, as a noise component included in the sub push-pull signal SPP, for example, a noise component caused by electromagnetic noise radiated from an electronic circuit, a noise caused by stray light from an optical element or a casing supporting the optical element, for example. And noise components due to stray light in other layers generated when the optical disc is a multilayer disc. Here, “other-layer stray light” refers to an information recording layer that is a target for recording or reproducing information among these information recording layers when the optical disc includes multiple information recording layers such as two or three layers. Means return light reflected by another different information recording layer.

  When the other layer stray light is detected by the light receiving surface that receives the return light beam of ± 1st order light, the light reception signal component of the other layer stray light is also amplified when the sub push-pull signal SPP is amplified. Generate an offset in the signal. Since the signal level of the noise component due to the other layer stray light is relatively high, the offset due to the other layer stray light is particularly problematic. In the conventional three-beam push-pull method, it is difficult to cancel the offset due to such other layer stray light.

  In view of the above, an object of the present invention is to provide an optical head capable of canceling an offset caused by an objective lens shift by using a light detection element having a light-receiving surface pattern with a simple configuration, and an optical disk apparatus equipped with the optical head. It is to be.

  In order to achieve the above object, an optical head according to the present invention includes a semiconductor laser, an objective lens for condensing a light beam emitted from the semiconductor laser to form a focused spot on an information recording layer of an optical disc, and a main lens. A light detecting element including a light receiving portion and a first sub light receiving portion, and a first diffraction region and a second diffraction region on both sides of a dividing line along a first direction corresponding to a tangential direction of the optical disc, An optical element that generates a zero-order diffracted light beam and a ± first-order diffracted light beam by receiving and transmitting and diffracting the return light beam reflected by the information recording layer of the optical disc in both the first diffraction region and the second diffraction region; The main light-receiving unit includes a first main light-receiving surface and a second main light-receiving surface arranged in a second direction corresponding to a radial direction of the optical disc so as to receive a light spot of the zero-order diffracted light beam. The first diffraction region has a grating structure in which the diffraction efficiency of the 0th-order and −1st-order transmitted diffracted light is higher than the diffraction efficiency of transmitted diffracted light of orders other than the 0th-order and −1st-order. And generating the −1st order diffracted light beam from the return light beam, and the second diffraction region has a transmission diffraction of 0th order and + 1st order transmitted diffracted light of orders other than the 0th order and + 1st order. The + 1st-order diffracted light beam is generated from the return light beam by having a grating structure higher than the diffraction efficiency of light, and the first sub-light-receiving unit is positioned to receive a part of the light spot of the + 1st-order diffracted light beam. Be placed.

  An optical disc apparatus according to the present invention includes the optical head for reading information from an optical disc or writing information to the optical disc.

  According to the present invention, based on the signal detected by the sub light receiving unit, a signal component corresponding to the offset caused by the objective lens shift is generated, and the push-pull signal from which the offset is removed using this signal component. Can be generated as a tracking error signal. This signal component can be detected using a light detection element having a light-receiving surface pattern with a simple configuration, such as a light detection element used for general purposes.

1 is a diagram schematically showing a main configuration of an optical disc device according to a first embodiment of the present invention. 2 is a diagram schematically showing a basic configuration of an optical head according to Embodiment 1. FIG. 2 is a diagram schematically showing an example of an optical element in Embodiment 1. FIG. FIG. 6 is a diagram schematically showing another example of the optical element in the first embodiment. FIG. 4 is a diagram schematically showing a light spot of a diffracted light beam formed by the optical element in Embodiment 1 and an example of a light receiving surface pattern of the light detection element. (A)-(c) shows roughly the positional relationship between the photon detection element and light spot in Embodiment 1, and shows light intensity distribution of the 0th-order reflected diffracted light of a light spot roughly. FIG. FIG. 6 is a diagram schematically showing another example of the light spot of the diffracted light beam formed on the optical element in the first embodiment. FIG. 6 is a diagram schematically showing another example of the light receiving surface pattern of the light detection element in the first embodiment. It is the schematic for demonstrating the positional relationship of the other-layer stray light and light receiving part which concern on Embodiment 2. FIG. It is the schematic for demonstrating the positional relationship of the other-layer stray light and light receiving part which concern on Embodiment 2. FIG. It is a figure which shows an example of the photon detection element with a general purpose light-receiving surface pattern used with a 3 beam push pull method. It is a figure which shows roughly the positional relationship of the general purpose light-receiving surface pattern and light spot which are used in Embodiment 3 which concerns on this invention. It is a figure which shows roughly the positional relationship of the general purpose light-receiving surface pattern used in Embodiment 3, and a light spot. It is a figure which shows schematically the basic composition of the optical head of Embodiment 4 which concerns on this invention.

  Hereinafter, various embodiments according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a diagram schematically showing the main configuration of the optical disc apparatus 50 according to the first embodiment. The optical disk device 50 includes a spindle motor 51, an optical head 52, a thread motor 53, a laser control circuit 54, a servo control circuit 55, a reproduction signal processing circuit 56, a demodulation circuit 60, a modulation circuit 64, a RAM (Random Access Memory) 80, and An MPU (Micro Processing Unit) 81 is provided. The MPU 81 executes various control processes according to commands from a host device (not shown).

  The servo control circuit 55 includes an optical head control circuit 61, a thread motor control circuit 62, and a spindle motor control circuit 63. These control circuits 61 to 63 operate in response to individual commands from the MPU 81. The reproduction signal processing circuit 56 includes a wobble signal detection circuit 57, a reproduction signal detection circuit (RF signal detection circuit) 58, and a servo signal detection circuit 59.

  The optical disk 5 is detachably mounted on a turntable fixed to a drive shaft (spindle) of the spindle motor 18. The spindle motor 51 rotates the optical disc 5 under the control of the spindle motor control circuit 63. Here, the spindle motor control circuit 63 operates in accordance with a command from the MPU 81, and controls the spindle servo so that the actual rotational speed matches the target rotational speed based on the pulse signal representing the actual rotational speed supplied from the spindle motor 51. Execute.

  The optical head 52 irradiates the optical disk 5 with the laser light beam IL, receives the return light beam reflected by the information recording layer of the optical disk 5, generates a signal, and outputs this signal to the reproduction signal processing circuit 56. . The optical disc 5 is a single-layer disc having a single information recording layer or a multilayer disc having a plurality of information recording layers. Specific examples of the optical disk 5 include, but are not limited to, a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc).

  The sled motor 53 receives the control of the sled motor control circuit 62 and transmits a rotational driving force to a feed mechanism such as a rack or a pinion, for example, thereby moving the frame 52C in the radial direction of the optical disc 5 (radial direction of the optical disc 5). Move. Since the optical head 52 is fixed to the frame 52C, it moves together with the frame 52C. The thread motor control circuit 62 operates according to a command from the MPU 81.

  The wobble signal detection circuit 57 has a function of detecting the wobble signal from the light receiving component of the reflected light from the meandering guide track groove in the optical disc 5. However, when the optical disk 5 is a read-only ROM (Read Only Memory) disk having no guide track groove, the function of the wobble signal detection circuit 57 is not required.

  The signal detected by the optical head 52 is output to the reproduction signal processing circuit 56 via a bus (not shown). In the reproduction signal processing circuit 56, the reproduction signal detection circuit 58 has a function of detecting a reproduction RF signal (reproduction signal) based on the signal received from the optical head 52. The demodulation circuit 60 demodulates the wobble signal output from the wobble signal detection circuit 57 and the reproduction signal output from the reproduction signal detection circuit 58 to generate a data signal DS. In addition, the reproduction signal detection circuit 58 generates data and a status signal representing the signal amplitude value of the reproduction signal, and outputs the data and the status signal to the MPU 81. Information (synchronization information and address information) obtained by demodulating the wobble signal is also output to the MPU 81 and the servo control circuit 55 and can be used.

  The servo signal detection circuit 59 generates various servo signals (for example, a focus error signal and a tracking error signal) for feedback control based on the signal received from the optical head 52. These servo signals SS are output to the optical head control circuit 61.

  The MPU 81 determines the overall operation of the optical disc apparatus 50 based on the signals supplied from each component in the reproduction signal processing circuit 56 and the servo control circuit 55, and gives control data to each component to give each component. Control the behavior. Note that there may be a configuration in which some of the components of the reproduction signal processing circuit 56 are processed by the MPU 81.

  The RAM 80 is provided with a program area 80A and a data area 80B. The MPU 81 reads a program stored in the program area 80A of the RAM 80, and executes the program using the data area 80B. Thereby, the MPU 81 can control the operation of each component in the optical disc apparatus 50 and can make a determination for control based on the signal output from each component.

  The optical head control circuit 61 operates according to a command from the MPU 81 and controls the operation of the optical head 52. Specifically, the optical head control circuit 61 generates a driving signal for focusing and tracking of the light beam IL based on a focus error signal and a tracking error signal included in the servo signal, and uses the driving signal for the optical head. It supplies to the actuator 9 (FIG. 2) in 52. The actuator 9 has a function of driving the objective lens 4 (FIG. 2) in the radial direction of the optical disc 5 and also in the focus direction (the optical axis direction of the objective lens 4) in response to the supply of the drive signal. Therefore, a focus servo loop and a tracking servo loop are formed by the optical head 52, the servo signal detection circuit 59, and the optical head control circuit 61.

  FIG. 2 is a diagram schematically showing the basic configuration of the optical head 52. As shown in FIG. 2, the optical head 52 includes a semiconductor laser 2, a beam splitter 3, an objective lens 4, an actuator 9, an optical element 6, and a light detection element 27. FIG. 2 shows the components of the detection optical system for the purpose of explaining the basic configuration and the operating principle of the optical head 52 of the present embodiment, but is limited to the configuration of FIG. Is not to be done. For example, the optical head 52 may include a sensor optical system for detecting the focus error amount and tracking error amount of the objective lens 4 with respect to the information recording layer of the optical disc 5.

  At the time of data reproduction, the laser control circuit 54 in FIG. 1 operates according to a command from the MPU 81 to control the semiconductor laser 2 (FIG. 2) in the optical head 52 and is necessary for data reproduction from the semiconductor laser 2. A laser beam having emission power is emitted. As shown in FIG. 2, the light beam EL emitted from the semiconductor laser 2 is irradiated onto the optical disk 5 through the beam splitter 3 and the objective lens 4.

  On the other hand, at the time of data recording, the modulation circuit 64 of FIG. 1 assigns an error correction code to the data output from the MPU 81 and performs data modulation to generate recording data. The modulation circuit 64 further generates a write strategy signal based on the recording data. The laser control circuit 54 controls the semiconductor laser 2 in the optical head 52 based on the write strategy signal, and emits laser light having light emission power necessary for data recording from the semiconductor laser 2.

  The light beam EL emitted from the semiconductor laser 2 is reflected by the beam splitter 3 and enters the objective lens 4. The objective lens 4 condenses the light beam incident from the beam splitter 3 on the information recording layer of the optical disc 5 to form a condensing spot on the information recording layer. The return light beam reflected by the optical disk 5 becomes a convergent light beam by the objective lens 4, passes through the beam splitter 3, and enters the optical element 6.

  The optical element 6 transmits and diffracts the return light beam incident from the beam splitter 3 to generate a 0th order diffracted light beam D0, a −1st order diffracted light beam D1a, and a + 1st order diffracted light beam D1b. FIG. 3 is a diagram schematically illustrating a configuration example of the optical element 6. As shown in FIG. 3, the optical element 6 has diffraction regions 601 and 602 on both sides of a dividing line 600 formed along the direction Y corresponding to the tangential direction of the optical disc 5. Since the return light beam reflected by the information recording layer of the optical disc 5 includes diffracted light (hereinafter referred to as “reflected diffracted light”) due to the periodic structure of the information track of the information recording layer, it is shown in FIG. As shown, the return light beam RL incident on both of the diffraction regions 601 and 602 of the optical element 6 includes a substantially circular 0th-order reflected diffracted light component RL0 and overlaps this 0th-order reflected diffracted light component RL0. A + 1st order reflected diffracted light component RL1 and a −1st order reflected diffracted light component RL2 are included.

  Since the dividing line 600 of the optical element 6 substantially coincides with the direction Y corresponding to the tangential direction of the optical disc 5, the + 1st order reflected diffracted light component RL1 is incident on one diffraction region 601, but the -1st order reflection. The diffracted light component is not incident. Further, although the −1st order reflected diffracted light component RL2 is incident on the other diffraction region 602, the + 1st order reflected diffracted light component is not incident. One diffraction region 601 has a grating structure in which the diffraction efficiency of the 0th-order and −1st-order transmitted diffracted light is higher than the diffraction efficiency of transmitted diffracted light of orders other than the 0th-order and −1st-order. A part of the 0th-order diffracted light beam D0 and the −1st-order diffracted light beam D1a can be generated from the light beam. The other diffraction region 602 has a grating structure in which the diffraction efficiency of the 0th-order and + 1st-order transmitted diffracted light is higher than the diffraction efficiency of transmitted diffracted light of orders other than the 0th-order and + 1st-order. The remaining portion of the first order diffracted light beam D0 and the + 1st order diffracted light beam D1b can be generated.

  Such an optical element 6 can be realized by using, for example, a transmissive blazed diffraction grating. The transmissive blazed diffraction grating is a diffraction grating having a grating groove having a sawtooth cross-sectional shape. The diffraction efficiency of each order of diffracted light can be adjusted by changing the blaze angle of the grating grooves. In the diffraction region 601 of FIG. 3, the blaze angle is determined so that the diffraction efficiency of the 0th-order and −1st-order transmitted diffracted light is higher than the diffraction efficiency of light of orders other than the 0th-order and −1st-order. In the diffraction region 602 of FIG. 3, the blaze angle is determined so that the diffraction efficiencies of the 0th-order and + 1st-order transmitted diffracted light are higher than the diffraction efficiencies of light of orders other than the 0th-order and + 1st-order. do it.

  As illustrated in FIG. 4, the optical element 6 may include a light shielding region 8 that surrounds the diffraction regions 601 and 602. The light shielding region 8 may be formed of a light reflecting film such as a metal thin film, a light absorbing film, or a diffraction grating. The light shielding region 8 can suppress deterioration of the received light signal due to stray light. Further, the diffraction regions 601 and 602 do not necessarily need to be in close contact with each other, and may be separated from each other by a tolerance associated with the processing of the diffraction surfaces of the diffraction regions 601 and 602.

  As shown in FIG. 2, the diffraction regions 601 and 602 of the optical element 6 irradiate the main light receiving portion 270 of the light detection element 27 with the light spot of the 0th-order diffracted light beam D0. Also, one diffraction region 601 generates a −1st order diffracted light beam D1a and irradiates this light spot onto the second sub-light-receiving portion 272 of the light detection element 27, and the other diffraction region 602 has a + 1st order diffracted light beam D1b. And the light spot is irradiated onto the first sub light receiving portion 271 of the light detecting element 27.

  FIG. 5 is a diagram schematically showing the arrangement of the light receiving portion of the light detection element 27 and the light spot of the diffracted light beam irradiated on the light detection element 27. As shown in FIG. 5, the light detecting element 27 receives a main light receiving portion 270 that receives the light spot QM of the 0th-order diffracted light beam D0 and a first light receiving surface that receives the light spot QS1 of the + 1st-order diffracted light beam D1b. 1 sub light receiving part 271 and 2nd sub light receiving part 272 which receives light spot QS2 of -1st order diffracted light beam D1a with a single light receiving surface. The main light receiving unit 270 is divided into first and second light receiving surfaces 2701 and 2702, and the first main light receiving surface 2701 and the second main light receiving surface 2702 correspond to a radial direction perpendicular to the tangential direction. They are arranged in the direction X. This direction X coincides with the direction of light diffraction by the optical element 6. The main light receiving unit 270 receives the 0th-order diffracted light beam D0 on both of the light receiving surfaces 2701 and 2702, generates electric signals MR and ML according to the received light amounts, and generates the electric signals MR and ML as a reproduction signal processing circuit. 56. Here, the first main light receiving surface 2701 outputs an electric signal ML, and the second main light receiving surface 2702 outputs an electric signal MR.

  In addition, the first sub light receiving unit 271 and the second sub light receiving unit 272 of the light detecting element 27 receive the + 1st order diffracted light beam D1a and the −1st order diffracted light beam D1b, respectively, and the electrical signal SL corresponding to the amount of received light. , SR are generated and the electric signals SL, SR are supplied to the reproduction signal processing circuit 56. The reproduction signal processing circuit 56 generates a servo signal SS based on the electrical signals MR, ML, SR, and SL as will be described later, and outputs the servo signal SS to the optical head control circuit 61.

  The main light receiving unit 270 includes a first main light receiving surface 2701 and a second main light receiving surface 2702 arranged so as to be adjacent to each other in the direction X. The light spot QM of the 0th-order diffracted light beam D0 on the main light receiving unit 270 has a substantially circular shape or an elliptical shape. The 0th-order diffracted light beam QM includes a 0th-order reflected diffracted light component Q0, and a + 1st-order reflected diffracted light component Q01 and a −1st-order reflected diffracted light component Q02 overlapping with the 0th-order reflected diffracted light component Q0. The ± first-order reflected diffracted light components Q01 and Q02 are attributed to the information track structure of the optical disc 5. The zero-order reflected diffracted light component Q0 is received by both the first main light receiving surface 2701 and the second main light receiving surface 2702. The −1st order reflected diffracted light component Q02 is received by the second main light receiving surface 2702, and the + 1st order reflected diffracted light component Q01 is received by the first main light receiving surface 2701. The first main light receiving surface 2701 and the second main light receiving surface 2702 respectively photoelectrically convert incident light and output electric signals ML and MR.

  On the other hand, the light spot QS2 of the −1st order diffracted light beam D1a has an arc shape or elliptical arc shape with a tip directed in the + 1st order diffraction direction as shown in FIG. Although the + 1st order reflected diffracted light component Q2a that overlaps this is included as a main component, the -1st order reflected diffracted light component is hardly included. The light spot QS1 of the + 1st order diffracted light beam D1b has an arc shape or elliptical arc shape having a tip directed in the −1st order diffraction direction, and overlaps with the 0th order reflected diffracted light component Q1. The reflection diffracted light component Q1a is included as a main component, but the + 1st order reflected diffracted light is hardly included.

  Further, as shown in FIG. 5, the first sub light receiving unit 271 is arranged at a position where it does not receive the entire light spot QS1 and does not receive the −1st order reflected diffracted light component Q1a corresponding to the push-pull component. ing. The second sub light receiving unit 272 is also arranged at a position where it does not receive all of the light spot QS2 and does not receive the + 1st order reflected diffracted light component Q2a corresponding to the push-pull component. In other words, the edge portion (the edge portion on the right side of the drawing) which is one end of the −1st order diffraction direction of the first sub light receiving portion 271 divides the light spot QS1 so that the −1st order reflected diffracted light component Q1a is not received. In addition, an edge portion (edge portion on the left side of the drawing) which is one end of the second sub light receiving unit 272 in the + 1st order diffraction direction also divides the light spot QS2 so that the + 1st order reflected diffracted light component Q2a is not received.

Next, a method for generating a push-pull signal will be described below. A push-pull signal is used for tracking servo for causing the irradiation light beam IL to the objective lens 4 to follow the information track. In the present embodiment, the push-pull signal PP is given by the following arithmetic expression (1).
_{PP = (S AD -S BC)} + k × (S E -S H) (1)

Here, S _AD is a light reception signal obtained from the output signal ML of the first main light receiving surface 2701, S _BC is a light reception signal obtained from the output signal MR of the second main light receiving surface 2702, and S _E is , a light reception signal obtained from the output signal SL of the first sub light receiving portion 271, S _H is a light reception signal obtained from the output signal SR of the second sub light receiving portion 272, represents respectively. k is a gain coefficient.

  FIGS. 6A to 6C schematically show the positional relationship between the light detection element 27 and the light spots QM, QS1, and QS2, as well as the main light receiving unit 270, the first sub light receiving unit 271, and It is a figure which shows roughly the light intensity distribution of the 0th-order reflected diffracted light component of the light spots QM, QS1, and QS2 in the second sub light receiving unit 272. FIG. 6A shows a state (reference state) when no objective lens shift occurs, and FIGS. 6B and 6C show a state when an objective lens shift occurs. Yes. The light intensity distributions of the zeroth-order reflected diffracted light components of the light spots QM, QS1, and QS2 are Gaussian distributions depending on the characteristics of the semiconductor laser, and form light intensity distributions G0, G1, and G2, respectively. Referring to FIGS. 6A to 6C, the light reception signal component of the first sub light receiving unit 271 corresponds to the shaded portion of the light intensity distribution G1, and the light reception signal component of the second sub light receiving unit 272 is This corresponds to the shaded portion of the light intensity distribution G2.

As shown in FIG. 6B, if the entire light spots QM, QS1, and QS2 move to the right from the position of the reference state with respect to the light detection element 27 by the objective lens shift, the light intensity distributions G0 and G1. , G2 peak position is also shifted to the right. At this time, the signal level of (S _AD −S _BC ) decreases, the signal level of (S _E −S _H ) increases (the amount of light received by the first sub light receiving unit 271 increases, and the second sub light receiving). The amount of light received by the portion 272 decreases). On the other hand, as shown in FIG. 6C, if the entire light spots QM, QS1, and QS2 move to the left from the position of the reference state with respect to the light detection element 27 by the objective lens shift, the light intensity distribution. The peak positions of G0, G1, and G2 are also shifted to the left. At this time, the signal level of (S _AD −S _BC ) increases, the signal level of (S _E −S _H ) decreases (the amount of light received by the first sub light receiving unit 271 decreases, and the second sub light reception). The amount of light received by the portion 272 increases).

_Therefore, it is found to have a (S AD _{-S BC)} and _{S E} has opposite _phases, (S AD _{-S BC)} and -S _H also opposite phases. Therefore, the offset due to the objective lens shift can be canceled by appropriately adjusting the gain coefficient k and amplifying the signal component of (S _E −S _H ).

Instead of the above formula (1), push-pull signals PPL and PPR given by the following formula (1a) or (1b) may be used.
PPL = (S _AD −S _BC ) + k × S _E (1a)
_{PPR = (S AD -S BC)} + k × (-S H) (1b)

  The optical head control circuit 61 controls the operation of the actuator 9 so that the level of the push-pull signal given by the above formula (1), (1a) or (1b) approaches zero, thereby changing the irradiation light beam IL to the information track. Can be followed.

Further, the reproduction signal S _RF can be generated according to the following arithmetic expression (2).
S _RF = S _AD + S _BC (2)

As shown in FIGS. 6B and 6C, the signal components S _AD and S _BC of the reproduction signal S _RF have opposite phases with respect to the objective lens shift, and thus both signal components S _AD and S _{BC are used.} The offset due to the objective lens shift is cancelled.

As described above, the reproduction signal processing circuit 56, based on the signals SL and SR detected by the first sub light receiving units 271 and 272, the signal component k × (S corresponding to the offset caused by the objective lens shift. _E− S _H ), k × S _E or k × (−S _H ) can be generated, and the push-pull signal PP, PPL or PPR from which the offset is removed can be generated using this signal component. The signal component can be easily generated by using the light detecting element 27 having a light receiving surface pattern with a simple configuration as shown in FIG. As shown in FIG. 5, the light spot Q1 of the + 1st order diffracted light beam D1a includes the −1st order reflected diffracted light component Q1a, but hardly includes the + 1st order reflected diffracted light component, so the first spot in the ± 1st order diffraction direction. It is easy to arrange the first sub light receiving unit 271 so as not to receive the −1st order reflected diffracted light component Q1a only by appropriately positioning the first sub light receiving unit 271. The light spot Q2 of the −1st order diffracted light beam D1b also includes the + 1st order reflected diffracted light component Q2a, but hardly includes the −1st order reflected diffracted light component, so that the second sub light receiving portion 272 is appropriately disposed in the ± 1st order diffracted direction. The second sub light receiving unit 272 can be easily arranged so as not to receive the + 1st order reflected diffracted light component Q2a only by positioning. Furthermore, each light receiving surface of the first sub light receiving unit 271 and the second sub light receiving unit 272 may be a single surface. Therefore, the light receiving surface pattern of the photodetecting element can have a simple structure.

  In addition, as described above, the three-beam push-pull method has a limitation in increasing the light intensity of the sub beam during data recording, which limits the cancellation of the offset superimposed on the push-pull signal. It was. In particular, when the optical disk 5 is a multi-layer disk, it is difficult to cancel the offset with high accuracy due to the presence of noise components caused by stray light from other layers.

  In contrast, the optical head according to the present embodiment does not use a sub beam, and there is no restriction on the diffraction efficiency of the optical element 6, so that the light intensity of the irradiation light beam IL can be increased during data recording. Therefore, the gain coefficient k in the above equations (1), (1a), and (1b) can be made sufficiently small. Therefore, compared with the three-beam push-pull method, it is possible to remove the offset from the push-pull signal with high accuracy.

  Further, the first sub light receiving unit 271 is arranged not to receive the + 1st order reflected diffracted light component Q1a, and the second sub light receiving unit 272 is arranged not to receive the −1st order reflected diffracted light component Q2a. For this reason, the areas of the light receiving surfaces of the first sub light receiving unit 271 and the second sub light receiving unit 272 can be reduced. Accordingly, it is possible to reduce the amount of other-layer stray light received by the first sub light receiving unit 271 and the second sub light receiving unit 272.

Incidentally, as described above, a push-pull signal based on the above formula (1a) or (1b) can be used instead of the above formula (1), but it is resistant to external noise, temperature change, and wavelength variation of the light beam. From the viewpoint of improving the above, it is preferable to use the above formula (1) rather than the above formula (1a) or (1b). With respect to external noise, the signal component _S E of the above equation (1), _{S H} have the same phase, the signal component _S E, the amount of change _{S H} respectively also substantially the same, the signal component _S E, _{S H} By taking the difference (= S _E −S _H ), it is possible to cancel the influence of external noise, temperature change, and wavelength variation of the light beam. The diffraction angles of the diffractive region 601 and the diffractive region 602 of the optical element 6 are adjusted to be substantially the same. However, the lattice spacing of the optical element 6 changes due to temperature changes, and the wavelength variation of the light beam. May occur, and the diffraction angle 601 and the diffraction region 602 may deviate in absolute value from each other. In this case, the irradiation position of the light spot QS1 and the light spot QS2 in FIG. 5 varies, and the amount of light received by the first sub light receiving unit 271 and the second sub light receiving unit 272 varies. The variation of such received light amount, the signal component _S E, can be canceled by taking the difference between _{S H (= S E -S H} ).

Modification of the first embodiment.
As a modification of the first embodiment, the optical element 6 may form the light spots QM, TS1, TS2 shown in FIG. 7 instead of forming the light spots QM, QS1, QS2 shown in FIG. . In this modification, one diffraction region 601 of the optical element 6 has a grating structure in which the diffraction efficiency of the 0th-order and + 1st-order transmitted diffracted light is higher than the diffraction efficiency of transmitted diffracted light of orders other than the 0th-order and + 1st-order. Therefore, a part of the 0th-order diffracted light beam and the + 1st-order diffracted light beam can be generated from the return light beam. The first sub-light-receiving unit 271 is irradiated with the light spot TS1 of the + 1st order diffracted light beam. Further, the other diffraction region 602 has a grating structure in which the diffraction efficiency of the 0th-order and −1st-order transmitted diffracted light is higher than the diffraction efficiency of the transmitted diffracted light of orders other than the 0th-order and −1st-order. The remaining portion of the 0th order diffracted light beam and the −1st order diffracted light beam can be generated from the light beam. The −1st order diffracted light beam is applied to the second sub light receiving unit 272.

  In this modified example, the first sub light receiving unit 271 is disposed at a position where it does not receive all of the light spot TS1 and does not receive the + 1st order reflected diffracted light T1a corresponding to the push-pull component. The second sub light receiving unit 272 is also arranged at a position where it does not receive all of the light spot TS2 and does not receive the −1st order reflected diffracted light T2a corresponding to the push-pull component.

Therefore, in this modification, the push-pull signal PP can be given by the following arithmetic expression (3).
_{PP = (S AD -S BC)} -k × (S E -S H) (3)

Alternatively, push-pull signals PPL and PPR given by the following arithmetic expression (3a) or (3b) may be used instead of the above expression (3).
PPL = (S _AD −S _BC ) −k × S _E (3a)
_{PPR = (S AD -S BC)} -k × (-S H) (3b)

  As in the case of the first embodiment, the above equation (3) is used rather than the above equation (3a) or (3b) from the viewpoint of improving the resistance to external noise, temperature change, and wavelength variation of the light beam. It is desirable.

  As another modification of the first embodiment, a configuration using the configuration shown in FIG. 8 may be used instead of the configuration of the photodetecting element 27 shown in FIG. The photodetector shown in FIG. 8 includes a main light receiving unit 270B, a first sub light receiving unit 271 and a second sub light receiving unit 272. The configurations of the first sub light receiving unit 271 and the second sub light receiving unit 272 are the same as those of the first sub light receiving unit 271 and the second sub light receiving unit 272 shown in FIG.

  The light receiving surface of the main light receiving unit 270B is divided into four light receiving surfaces 2701a, 2701b, 2702a, and 2702b. The light receiving surfaces 2701a and 2701b are arranged along the direction Y corresponding to the tangential direction of the optical disc 5, and the light receiving surfaces 2702a and 2702b are also arranged along the direction Y corresponding to the tangential direction.

In this modification, the push-pull signal is given by the following arithmetic expression (4), (4a) or (4b).
PP = (S _A + S _B ) − (S _C + S _D ) + k × (S _E −S _H ) (4)
PPL = (S _A + S _B ) − (S _C + S _D ) + k × S _E (4a)
PPR = (S _A + S _B ) − (S _C + S _D ) + k × (−S _H ) (4b)

Here, _{S A} is a light receiving signal obtained from the output signal MA of the light receiving surface 2701a, _{S B} is a light reception signal obtained from the output signal MB of the light-receiving surface 2701 b, _{S C,} the output of the light receiving surface 2702a a light reception signal obtained from the signal MC, S _D is a light receiving signal obtained from the output signal MD of the light-receiving surface 2702 b, represents respectively. k is a gain coefficient.

Further, the focus error signal FES based on the astigmatism method can be obtained by the following arithmetic expression (5).
FES = (S _B + S _C ) − (S _A + S _D ) (5)

In the light detection element of this modification, when the light spots TS1 and TS2 are formed as shown in FIG. 7, push-pull signals are expressed by the following arithmetic expressions (6), (6a) and (6b). ).
_{PP = (S A + S B} -S C -S D) -k × (S E -S H) (6)
PPL = (S _A + S _B −S _C −S _D ) −k × S _E (6a)
_{PPR = (S A + S B} -S C -S D) -k × (-S H) (6b)

Embodiment 2. FIG.
Next, a second embodiment will be described. In the present embodiment, the arrangement of the main light receiving unit 270, the first sub light receiving unit 271 and the second sub light receiving unit 272 in the light detection element 27 of the first embodiment is optimized. FIG. 9 is a diagram schematically showing a positional relationship between the other layer stray light generated when the optical disk 5 is a two-layer disk and the light receiving unit. FIG. 10 is a diagram schematically showing the arrangement of the light receiving units that can reduce noise caused by the other layer stray light generated when the optical disc 5 is a two-layer disc.

  As shown in FIG. 9, the optical axis of the other-layer stray light SLt coincides with the optical axis of the return light beam D0 that forms the light spot QM, and the irradiation region of the other-layer stray light SLt is centered on the optical axis. This is a circular region having a radius R. Since the other-layer stray light SLt leaks into the areas of the first sub-light-receiving unit 271 and the second sub-light-receiving unit 272, a noise component due to the other-layer stray light SLt is superimposed on the push-pull signal.

  The other-layer stray light SLt is the same as the return light generated when the condensing point of the irradiation light beam IL is moved by the layer interval of the information recording layer of the optical disc 5 to be in the defocused state. For this reason, as the layer interval of the information recording layer becomes shorter, the area of the irradiation region of the other layer stray light SLt in the light detection element 27 becomes smaller, and the light density in the irradiation region becomes lower. Therefore, if the amount of the other layer stray light SLt leaking into the areas of the first sub light receiving portion 271 and the second sub light receiving portion 272 is set to a sufficiently small light amount with respect to the objective lens shift amount, the other layer stray light SLt is generated. The influence on the push-pull signal can be suppressed.

  Therefore, as shown in FIG. 10, the main light receiving unit 270 and the second sub light receiving unit so that the first sub light receiving unit 271 and the second sub light receiving unit 272 are arranged outside the irradiation region of the other layer stray light SLt. It is desirable to provide a distance W between The same is true between the main light receiving unit 270 and the first sub light receiving unit 271.

Here, for example, consider a case where the total amount of the return light beam reflected by each information recording layer of the optical disc 5 is substantially the same. With respect to the push-pull signal, the ratio (allowable ratio) of the received light amount of the other layer stray light SLt is x, and the spectral ratios (0th: 1st) of the diffraction regions 601 and 602 of the optical element 6 are S0: When S1 is set, the radius of the light spot QM is r, and the radius of the irradiation region of the other layer stray light SLt is R, if the following relational expression (7) is satisfied, the other layer stray light SLt is converted into the first sub light receiving unit 271. Even if it leaks into the second auxiliary light receiving portion 272, it can be ignored.
x> (r ² / R ² ) / (S1 / S0) (7)

  Here, S0 ≧ S1. Therefore, when this relational expression (7) is not satisfied, the first sub light receiving unit 271 and the second sub light receiving unit 272 are disposed outside the irradiation region of the other layer stray light SLt (the irradiation region of the other layer stray light SLt). When the distance W is set and the relational expression (7) is established, the first sub light receiving unit 271 and the second sub light receiving unit 272 are arranged so as to overlap with the irradiation region of the other layer stray light SLt. can do. Note that the value of x affects the tracking servo control, and detrack (track deviation) occurs by the value of x. For example, in the case of BD (Blu-ray Disc), the value allowed for this detrack is generally about ± 20 nm at most with respect to the track pitch of 320 nm, and therefore the value of x is preferably 0.1 or less.

A method for deriving the above equation (7) will be described below. In the multilayer optical disk 5, a case is considered in which the total amount of the return light beam reflected by each information recording layer is substantially the same. In this case, it can be considered that the total amount of light received by the light detection element 27 is substantially equal for the return light reflected by the target information recording layer in the optical disc 5 and the return light reflected by other information recording layers. Therefore, when the light density of the light spot QM of the 0th-order diffracted light is P0 and the light density of the other-layer stray light SLt is Ps, the following expression (7a) is established.
P0 × π × r ² = Ps × π × R ² (7a)

If this equation (7a) is modified, the following equation (7b) is derived.
Ps / P0 = r ² / R ² (7b)

On the other hand, considering the spectral ratio (approximately S0: S1) of the optical element 6, the relationship between the light density P0 of the light spot QM and the light densities P1 of the light spots QS1 and QS2 of the first-order diffracted light is expressed by the following formula ( 4c).
P0 / P1 = S0 / S1 (7c)

The offset cancellation by the objective lens shift utilizes the fact that the moving amount of the light spot QM of the 0th-order diffracted light and the moving amount of the light spots QS1 and QS2 of the 1st-order diffracted light are equal. Therefore, the gain coefficient k can be expressed by the following equation (7d) using the respective light densities P0 and P1.
k = P0 / P1 = S0 / S1 (7d)

Since the received light amount of the first-order diffracted light spots QS1 and QS2 in the first sub-light-receiving unit 271 and the second sub-light-receiving unit 272 is multiplied by k, it leaks into the first sub-light-receiving unit 271 and the second sub-light-receiving unit 272. However, the other layer stray light SLt (noise component) is also multiplied by k. Therefore, k × Ps × C _L (C _L : total light receiving area) is a noise component.

At this time, since the total light receiving area C _L depends on the arrangement of the light receiving surface, it is difficult to strictly define the total light receiving area C _L. Therefore, the light receiving total area C _L is approximately considered to be about light receiving area of the first order reflection diffraction light components Q01, Q02 comprising a push-pull component of the 0-order diffracted light. Thereby, the ratio of the other-layer stray light SLt can be regarded as approximately k × Ps / P0. When this ratio (= k × Ps / P0) is smaller than the allowable ratio x, even if the other-layer stray light SLt leaks into the first sub-light-receiving unit 271 and the second sub-light-receiving unit 272, this can be ignored. . That is, the following equation (7e) may be satisfied.
x> k × Ps / P0 (7e)

  If the above equations (7d) and (7c) are used, the above equation (7e) can be transformed into the above equation (7).

The value of S1 may be set large so as to satisfy the relational expression (7). For example, when S1 is substantially equal to S0, a relational expression of R> r / x ^1/2 can be derived from the relational expression (7). When this relational expression is established, the influence of the other layer stray light SLt can be ignored, so that the first sub light receiving unit 271 and the second sub light receiving unit 272 overlap with the irradiation region of the other layer stray light SLt. Can be arranged. On the other hand, when the relational expression R ≦ r / x ^1/2 is satisfied, the first sub light receiving portion 271 and the second sub light receiving portion 272 are arranged outside the irradiation region of the other layer stray light SLt. It is desirable to set the distance W.

  As described above, according to the second embodiment, the arrangement of the main light receiving unit 270, the first sub light receiving unit 271 and the second sub light receiving unit 272 in the light detection element 27 can be optimized.

Embodiment 3 FIG.
Next, Embodiment 3 will be described. The configuration of the optical head of the third embodiment is substantially the same as that of the optical head 52 of the first embodiment shown in FIG. As will be described below, if a photodetector having a general-purpose light receiving pattern is used instead of the photodetector 27, the manufacturing cost of the optical head can be reduced.

  FIG. 11 is a schematic diagram showing a photodetecting element 27B having a general-purpose light-receiving surface pattern used in the three-beam push-pull method. The photodetecting element 27B shown in FIG. 11 includes a main light receiving unit 270B that receives the return light beam MB corresponding to the main beam, a first sub light receiving unit 271B that receives the return light beams SB1 and SB2 corresponding to the sub beams, and 2nd sub light-receiving part 272B. The light receiving surface of the main light receiving unit 270B is divided into four light receiving surfaces 2701a, 2701b, 2702a, and 2702b. The light receiving surfaces 2701a and 2701b are arranged along the direction Y corresponding to the tangential direction of the optical disc 5, and the light receiving surfaces 2702a and 2702b are also arranged along the direction Y. The first sub light receiving unit 271 </ b> B is divided into two light receiving surfaces 2711 and 2712, and these light receiving surfaces 2711 and 2712 are arranged along a direction X corresponding to the radial direction of the optical disc 5. Similarly, the first sub light receiving portion 272 </ b> B is divided into two light receiving surfaces 2721 and 2722, and these light receiving surfaces 2721 and 2722 are arranged along a direction X corresponding to the radial direction of the optical disk 5.

When this photodetecting element 27B is used, the push-pull signal PP _3B is given by the following arithmetic expression (8) using the main push-pull signal MPP and the sub push-pull signal SPP.
PP _3B = MPP-α × SPP (8)
The main push-pull signal MPP and the sub push-pull signal SPP are as follows.
MPP = (S _A + S _B ) − (S _D + S _C ),
_{SPP = (S E -S F)} + (S G -S H)

Here, _{S A} is a light receiving signal obtained from the output signal MA of the light receiving surface 2701a, _{S B} is a light reception signal obtained from the output signal MB of the light-receiving surface 2701 b, _{S C,} the output of the light receiving surface 2702a a light reception signal obtained from the signal MC, _{S D} is a light receiving signal obtained from the output signal MD of the light-receiving surface 2702 b, _{S E} is a light reception signal obtained from the output signal SLa of the light receiving surface 2711, _{S F} is a light reception signal obtained from the output signal SLb of the light receiving surface 2712, _{S G} is a light reception signal obtained from the output signal SRa of the light receiving surface 2721, _{S H} is obtained from the output signal SRb of the light receiving surface 2722 The received light signals are respectively shown. α is a gain coefficient.

Further, the focus error signal FES based on the astigmatism method can be obtained by the following arithmetic expression (9).
FES = (S _B + S _C ) − (S _A + S _D ) (9)

The push-pull signal PP according to the present embodiment can be generated using the photodetecting element 27B having such a general light receiving surface pattern. As shown in FIG. 12, when the optical element 6 emits light spots QM, QS1, and QS2 similar to those shown in FIG. 5, the push-pull signal PP is given by the following arithmetic expression (10). .
PP = (S _A + S _B ) − (S _D + S _C ) + k × (S _E −S _H ) (10)

  Here, k is a gain coefficient.

On the other hand, as shown in FIG. 13, when the optical element 6 irradiates the same light spots QM, TS1, TS2 as those shown in FIG. 7, the push-pull signal PP is expressed by the following equation (11). Given.
PP = (S _A + S _B ) − (S _D + S _C ) −k × (S _E −S _H ) (11)

  The focus error signal FES can be generated based on the above equation (9) as in the three-beam push-pull method.

  As described above, according to the optical head of the third embodiment, the push-pull signal from which the offset is removed with high accuracy is generated by using the light detecting element having the light receiving surface pattern having a general-purpose and simple configuration. Can do.

  As described in the first embodiment, the other-layer stray light SLt has an optical axis that substantially coincides with the light spot QM of the return light beam D0. In order to prevent the signal component of the other-layer stray light SLt from leaking into the push-pull signal PP, the light spot of the first-order diffracted light beam may be formed at a position farther from the optical axis center of the other-layer stray light SLt. desirable. From this viewpoint, the configuration of FIG. 13 is preferable to the configuration of FIG.

  As shown in FIGS. 12 and 13, the main light receiving portion 270B is divided into four light receiving surfaces 2701a, 2701b, 2702a, and 2702b, but the number of light receiving surfaces is not limited to this.

Embodiment 4 FIG.
Next, a fourth embodiment will be described. FIG. 14 is a diagram schematically showing a basic configuration of the optical head 52B of the fourth embodiment. As shown in FIG. 14, the optical head 52B includes a semiconductor laser 2, a polarization beam splitter 3B, an objective lens 4, an optical element 6B, a quarter-wave plate 7, and a light detection element 27. The optical head 52B has the same drive means (not shown) as the actuator 9 in FIG. This optical head 52B is incorporated in the optical disc apparatus 50 in place of the optical head 52 of FIG.

  As shown in FIG. 14, the light beam EL emitted from the semiconductor laser 2 is reflected by the polarization beam splitter 3 </ b> B, and sequentially passes through the optical element 6 </ b> B, the quarter wavelength plate 7, and the objective lens 4 to the optical disk 5. Irradiated. Here, the polarization beam splitter 3B converts the outgoing light beam EL into linearly polarized light and emits it to the optical element 6B. The light beam transmitted through the optical element 6 </ b> B is converted into circularly polarized light by the quarter wavelength plate 7 and then condensed on the information recording layer of the optical disk 5 by the objective lens 4. The return light beam reflected by the optical disk 5 becomes a convergent light beam by the objective lens 4 and is converted to linearly polarized light by the quarter wavelength plate 7. Here, the polarization direction of the linearly polarized light that is the return light beam from the quarter wavelength plate 7 toward the polarization beam splitter 3B is the polarization direction of the linearly polarized light that is the irradiation light beam that is directed from the polarization beam splitter 3B to the quarter wavelength plate 7. Orthogonal to the direction.

  Similar to the optical element 6 of the first embodiment, the optical element 6B includes a diffraction region 601B having high diffraction efficiency of −1st order and 0th order light, and a diffraction region 602B having high diffraction efficiency of + 1st order and 0th order light. And have. The diffraction regions 601B and 602B irradiate the main light receiving portion 270 of the light detecting element 27 with a light spot of the 0th-order diffracted light beam DP0 generated by transmitting and diffracting the return light beam. Also, one diffraction region 601B irradiates the light spot of the −1st order diffracted light beam DP1a onto the second sub light receiving portion 272 of the light detection element 27, and the other diffraction region 602B light spot of the + 1st order diffracted light beam DP1b. Is irradiated onto the first sub light receiving portion 271 of the light detecting element 27. The optical element 6B can irradiate the light detection element 27 with light spots QM, QS1, QS2 or QM, TS1, TS2 as shown in FIG.

  As described above, according to the optical head of the fourth embodiment, it is possible to generate a push-pull signal with a small noise component using a light detection element having a light receiving surface pattern with a simple configuration. Furthermore, the optical head of Embodiment 4 can improve the light use efficiency by making the polarization direction of the irradiation light beam orthogonal to the polarization direction of the return light beam.

Modified example of the first to fourth embodiments.
The said Embodiment 1-4 is an illustration of this invention, and can also employ | adopt various forms other than the above. For example, the diffraction regions 601 and 602 shown in FIG. 3 have a rectangular shape, but are not limited thereto. The diffraction region of the optical element 6 only needs to have an area and shape that do not lack the light spot shape of the return light beam RL shown in FIG. 3 even if the objective lens shift occurs. It may be circular.

  In the first to fourth embodiments, the light detection element 27 includes the main light receiving unit 270, the first sub light receiving unit 271, and the second sub light receiving unit 272. As described above, the offset caused by the objective lens shift can be calculated using only one of the detection signals SR and SL of the first sub light receiving unit 271 and the second sub light receiving unit 272. In this case, the light detection element 27 does not have to include both the first sub light receiving unit 271 and the second sub light receiving unit 272, and only one of them may be included.

  As shown in FIG. 2, the optical element 6 is disposed on the optical path of the return light beam between the beam splitter 3 and the light detection element 27, but the present invention is not limited to this. The optical element 6 can be disposed at an arbitrary position on the optical path of the return light beam from the optical disk 5, that is, on the optical path between the optical disk 5 and the light detection element 27. When the optical element 6 is disposed between the beam splitter 3 and the objective lens 4, both the irradiation light beam IL and the return light beam pass through the optical path between the beam splitter 3 and the objective lens 4. It is necessary to have a surface. If the optical element 6 is arranged as shown in FIG. 2, there is an advantage that it is not necessary to form such a polarization selective diffraction surface.

  The diffraction pattern of the optical element 6 is not limited to the diffraction pattern shown in FIGS. 3 and 4 as long as the above-described effects can be obtained, and various modifications can be made.

  2 semiconductor laser, 3 beam splitter, 3B polarization beam splitter, 5 optical disk, 4 objective lens, 6, 6B optical element, 601, 602 diffraction area, 7 1/4 wavelength plate, 8 light shielding area, 9 actuator, 9C lens holder, 27 Photodetector, 50 Optical disk device, 51 Spindle motor, 52 Optical head, 53 Thread motor, 54 Laser control circuit, 55 Servo control circuit, 56 Reproduction signal processing circuit, 57 Wobble signal detection circuit, 58 Reproduction signal detection circuit, 59 Servo signal detection circuit, 60 demodulation circuit, 61 optical head control circuit, 62 thread motor control circuit, 63 spindle motor control circuit, 64 modulation circuit, 80 RAM, 81 MPU, 270 main light receiving unit, 271 first sub Light unit, 272 second sub light receiving portion, 2701 a first main light receiving surface, 2702 the second main light receiving surface.

Claims (15)

A semiconductor laser;
An objective lens for condensing the light beam emitted from the semiconductor laser to form a condensing spot on the information recording layer of the optical disc;
A light detecting element including a main light receiving portion and a first sub light receiving portion;
A first diffractive region and a second diffractive region on each side of a dividing line along a first direction corresponding to the tangential direction of the optical disc, and the return light beam reflected by the information recording layer of the optical disc An optical element that receives and transmits and diffracts light in both the first diffraction region and the second diffraction region to generate a zero-order diffracted light beam and a ± first-order diffracted light beam,
The main light receiving unit has a first main light receiving surface and a second main light receiving surface arranged in a second direction corresponding to a radial direction of the optical disc so as to receive a light spot of the 0th-order diffracted light beam,
The first diffraction region has a grating structure in which the diffraction efficiency of the 0th-order and −1st-order transmitted diffracted light is higher than the diffraction efficiency of transmitted diffracted light of orders other than the 0th-order and −1st-order. Generating the -1st order diffracted light beam from the beam;
The second diffraction region has a grating structure in which the diffraction efficiency of the 0th-order and + 1st-order transmitted diffracted light is higher than the diffraction efficiency of the transmitted diffracted light of orders other than the 0th-order and + 1st-order. Generating the + 1st order diffracted light beam;
The optical head according to claim 1, wherein the first sub light receiving unit is disposed at a position for receiving a part of the light spot of the + 1st order diffracted light beam.   2. The optical head according to claim 1, wherein the light detection element further includes a second sub light receiving portion disposed at a position for receiving a part of the light spot of the −1st order diffracted light beam. Light head. The optical head according to claim 1,
The light spot of the + 1st order diffracted light beam includes a 0th order reflected diffracted light component and a −1st order reflected diffracted light component caused by an information track of the information recording layer,
The optical head according to claim 1, wherein the first sub-light receiving unit is disposed at a position where the first-order reflected diffracted light component is not received. The optical head according to claim 2,
The light spot of the + 1st order diffracted light beam includes a 0th order reflected diffracted light component and a −1st order reflected diffracted light component caused by an information track of the information recording layer,
The first auxiliary light receiving unit is disposed at a position where the first-order reflected diffracted light component is not received,
The light spot of the −1st order diffracted light beam includes a 0th order reflected diffracted light component and a + 1st order reflected diffracted light component caused by an information track of the information recording layer,
2. The optical head according to claim 1, wherein the second sub light receiving unit is disposed at a position where the + 1st order reflected diffracted light component is not received. The optical head according to claim 1,
The light spot of the + 1st order diffracted light beam includes a 0th order reflected diffracted light component and a + 1st order reflected diffracted light component resulting from the information track of the information recording layer,
The optical head according to claim 1, wherein the first sub light receiving unit is disposed at a position where the first-order reflected diffracted light component is not received. The optical head according to claim 2,
The light spot of the + 1st order diffracted light beam includes a 0th order reflected diffracted light component and a + 1st order reflected diffracted light component resulting from the information track of the information recording layer,
The first sub-light-receiving unit is disposed at a position where the first-order reflected diffracted light component is not received;
The light spot of the -1st order diffracted light beam includes a 0th order reflected diffracted light component and a -1st order reflected diffracted light component resulting from the information track of the information recording layer,
2. The optical head according to claim 1, wherein the second sub light receiving unit is disposed at a position where the first-order reflected diffracted light component is not received. The optical head according to any one of claims 1, 3, and 5,
The optical disc is a multilayer disc having a plurality of information recording layers,
The allowable ratio of the amount of stray light received due to another information recording layer different from the information recording layer on which the light condensing spot is formed among the plurality of information recording layers is x, and the 0th order vs. 1st order of the optical element Is set to S1 / S0 (S0 ≧ S1), the radius of the light spot of the 0th-order diffracted light beam formed in the main light receiving unit is set to r, and the radius of the stray light irradiation region in the photodetecting element is set to R. And when
The first auxiliary light receiving unit is
x> (r ² / R ² ) / (S1 / S0),
The optical head is arranged so as to overlap with the stray light irradiation area when the relational expression is satisfied, and arranged so as not to overlap with the stray light irradiation area when the relational expression is not satisfied. The optical head according to any one of claims 1, 3, and 5,
The optical disc is a multilayer disc having a plurality of information recording layers,
The acceptable ratio of the amount of stray light received due to another information recording layer different from the information recording layer in which the condensing spot is formed among the plurality of information recording layers is x, and is formed in the main light receiving unit. When the radius of the light spot of the zero-order diffracted light beam is r, and the radius of the stray light irradiation region in the light detection element is R,
The first auxiliary light receiving unit is
R> r / x ^1/2 ,
The optical head is arranged so as to overlap with the stray light irradiation area when the relational expression is satisfied, and arranged so as not to overlap with the stray light irradiation area when the relational expression is not satisfied. The optical head according to any one of claims 2, 4, and 6,
The optical disc is a multilayer disc having a plurality of information recording layers,
The allowable ratio of the amount of stray light received due to another information recording layer different from the information recording layer on which the light condensing spot is formed among the plurality of information recording layers is x, and the 0th order vs. 1st order of the optical element Is set to S1 / S0 (S0 ≧ S1), the radius of the light spot of the 0th-order diffracted light beam formed in the main light receiving unit is set to r, and the radius of the stray light irradiation region in the photodetecting element is set to R. And when
The first sub light receiving unit and the second sub light receiving unit are:
x> (r ² / R ² ) / (S1 / S0),
The optical head is arranged so as to overlap with the stray light irradiation area when the relational expression is satisfied, and arranged so as not to overlap with the stray light irradiation area when the relational expression is not satisfied. The optical head according to any one of claims 2, 4, and 6,
The optical disc is a multilayer disc having a plurality of information recording layers,
The acceptable ratio of the amount of stray light received due to another information recording layer different from the information recording layer in which the condensing spot is formed among the plurality of information recording layers is x, and is formed in the main light receiving unit. When the radius of the light spot of the zero-order diffracted light beam is r, and the radius of the stray light irradiation region in the light detection element is R,
The first sub light receiving unit and the second sub light receiving unit are:
R> r / x ^1/2 ,
The optical head is arranged so as to overlap with the stray light irradiation area when the relational expression is satisfied, and arranged so as not to overlap with the stray light irradiation area when the relational expression is not satisfied. The optical head according to claim 2,
Each of the first main light receiving surface and the second main light receiving surface includes a plurality of light receiving surfaces arranged in the first direction,
Each of the first sub light receiving part and the second sub light receiving part comprises a single light receiving surface. The optical head according to claim 6, wherein
Each of the first sub light receiving unit and the second sub light receiving unit includes a plurality of light receiving surfaces arranged in the second direction,
The first diffraction region irradiates a light spot of the −1st order diffracted light beam on a light receiving surface arranged at a position farthest from the main light receiving portion among the plurality of light receiving surfaces included in the second sub light receiving portion. And
The second diffraction region irradiates a light spot of the + 1st order diffracted light beam on a light receiving surface disposed at a position farthest from the main light receiving portion among the plurality of light receiving surfaces included in the first sub light receiving portion. ,
An optical head characterized by that.   13. The optical head according to claim 1, wherein the optical element is a blazed diffraction grating having a grating groove having a sawtooth cross-sectional shape.   14. An optical disc apparatus comprising the optical head according to claim 1, wherein the optical head reads information from an optical disc or writes information to the optical disc. 15. The optical disc device according to claim 14, wherein
A disk drive for rotating the optical disk;
Based on the signal detected by the sub light receiving unit, a signal component corresponding to a DC offset component caused by the objective lens shift is generated,
A servo control unit that generates a tracking error signal based on a difference between signals detected on the first main light receiving surface and the second main light receiving surface and the signal component;
An actuator that receives a drive signal from the outside and shifts the objective lens at least in the radial direction of the optical disc by an amount according to the value of the drive signal; and
The optical disc apparatus, wherein the servo control unit controls the operation of the actuator using the tracking error signal as the drive signal.

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