JP2011187133A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device that properly records or reproduces information to/from different two or more kinds of optical disks while reducing the size and cost. <P>SOLUTION: A first luminous flux and a second luminous flux pass through a liquid crystal element LCD, to change the light emitting direction. The luminous fluxes can be properly made incident in a first light receiving part and a second light receiving part of a photodetector PD. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus capable of recording and / or reproducing information interchangeably with different types of optical disks.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB) It is possible to record 25 GB of information per layer on an optical disc having a diameter of 12 cm which is the same size as the above.

  By the way, it can not be said that the value of an optical disc player / recorder (optical information recording / reproducing device) as a product is sufficient only by appropriately recording / reproducing information on such a high-density optical disc. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information on high-density optical discs. Similarly, making it possible to appropriately record / reproduce information on DVDs and CDs leads to an increase in commercial value as an optical disc player / recorder for high-density optical discs. From such a background, an optical pickup device mounted on an optical disc player / recorder for high density optical discs can appropriately receive information while maintaining compatibility with both high density optical discs, DVDs, and even CDs. It is desired to have a performance capable of recording / reproducing.

  As a method for recording / reproducing information appropriately while maintaining compatibility with both high-density optical discs and DVDs, and even CDs, optical systems for high-density optical discs and optical systems for DVDs and CDs are used. A method of selectively switching the system to and from the recording density of an optical disk for recording / reproducing information is conceivable, but a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.

  Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, the optical system for high-density optical discs and the optical system for DVDs and CDs must be shared in compatible optical pickup devices. It is preferable to reduce the number of optical components constituting the optical pickup device as much as possible. In addition, it is most advantageous for miniaturization and cost reduction of the configuration of the optical pickup device to make the objective optical element arranged facing the optical disc as common as possible.

  Patent Documents 1 and 2 disclose a high-density optical disk using a light source and a common photodetector that house a semiconductor laser capable of emitting light beams of three different wavelengths in one package in order to reduce the size and cost. And an optical pickup device for recording and / or reproducing information so as to be compatible with conventional DVDs and CDs.

JP 2005-327403 A JP 2006-99941 A JP 2006-269987 A

  Thus, if a light source in which three semiconductor lasers are housed in one package is used, the optical system can be shared, and the optical pickup device can be made compact and low in cost. However, when a light source in which three semiconductor lasers are housed in one package is used, there are problems as described below.

  Patent Document 3 discloses a light source in which three semiconductor lasers are housed in one package. According to Patent Document 3, a so-called blue-violet semiconductor laser that emits a light beam of about 405 nm is formed on a GaN substrate, but a so-called red semiconductor laser that emits a light beam of about 655 nm and a so-called blue semiconductor laser that emits a light beam of about 785 nm. An infrared semiconductor laser is formed on a GaAs substrate. Here, when different semiconductor lasers are formed on the same substrate (referred to as a monolithic structure), the light emitting point can be positioned with relative accuracy in the optical axis direction with relative ease.

  In the light source of the three-wavelength laser one package having such a configuration, the monolithic two-wavelength laser element can be accurately positioned in the optical axis direction, while the remaining one-wavelength laser element is different from other two-wavelength chips. Since it is provided on the chip, it is difficult to accurately provide the positions of the remaining one-wavelength laser elements in the optical axis direction relative to the positions of the other two-wavelength laser elements. In particular, when the position of the light source with one wavelength that is not monolithic is different in the optical axis direction compared to the remaining light sources, the condensing position of the light beam with one wavelength that is not monolithic in the light receiving unit This is different from the light collecting position. As a result, when a single photodetector is used, the reflected light from the optical disk is appropriately reflected on the light receiving element when the light emitted from the objective lens forms an image on the optical disk for the emitted light from one light source. Even though the light beam can be adjusted to be condensed, all three light beams cannot be condensed similarly on the light receiving surface for detecting the focus error. Therefore, for light of a certain wavelength, an appropriate focus detection signal is obtained at the light receiving unit, and an appropriate focus detection signal is obtained. As a result, there is a problem that an appropriate optical disc reproduction signal cannot be obtained as a spot, or an offset occurs in the focus detection signal due to a focused spot having a shape shape different from a predetermined size in the focus error detection signal light receiving unit. .

  Further, the first semiconductor laser is provided on a common support substrate plane in a separate form from the second and third semiconductor lasers, or is provided with a common flat support substrate interposed therebetween. The light emitting point position of these semiconductor lasers may cause a manufacturing deviation not only in the optical axis direction but also in a direction perpendicular to the optical axis and parallel to the semiconductor laser bonding surface with respect to the support substrate (referred to as the x direction). On the other hand, since the second and third semiconductor lasers have a monolithic structure provided on the same chip, it can be said that there is almost no deviation of the emission point position between the two wavelengths in the x direction as in the z direction.

  In such a case, with respect to the light receiving portion for receiving the light beams having the wavelengths λ1, λ2, and λ3 provided in the same light receiving element, the light beams having the wavelengths λ2 and λ3 are positioned at appropriate light receiving portion positions in the x direction. If the three-wavelength light source is adjusted so as to collect the reflected light from the optical disk, it is difficult to collect the light at the wavelength λ1 at an appropriate position. If the three-wavelength light source is adjusted so as to collect the reflected light, it is difficult to collect the light beams having the wavelengths λ2 and λ3 at appropriate positions. On the other hand, if the photodetectors are provided separately, the above-described problems can be solved. However, providing a plurality of photodetectors complicates the optical path leading to the photodetectors, increasing the number of parts and increasing the cost. A new problem arises. A similar problem may occur in a light source in which two light emitting units that emit light beams having different wavelengths are arranged on different chips.

  The present invention has been made in consideration of the above-described problems, and provides an optical pickup device capable of appropriately recording / reproducing information on two or more different types of optical discs while reducing the size and reducing the cost. Objective.

The objective optical element according to claim 1 includes a single light-emitting unit that emits a first light beam having a wavelength λ1 and a second light-emitting unit that emits a second light beam having a wavelength λ2 (λ1 <λ2). A light source, an objective optical system, a photodetector, and a liquid crystal element, and the light beam from the first light emitting unit is condensed on the information recording surface of the first optical disk by the objective optical system. The reflected light is received by the photodetector through the liquid crystal element, and information is recorded and / or reproduced on the first optical disc based on a signal from the photodetector. The light beam from the second light emitting unit is condensed on the information recording surface of the second optical disk by the objective optical system to form a spot, and the reflected light is transmitted to the photodetector through the liquid crystal element. And receiving the second optical data based on a signal from the photodetector. In the recording and / or an optical pickup apparatus for reproducing information to disk,
The photodetector includes a first light receiving unit that receives the first light beam, and a second light receiving unit that receives the second light beam,
The liquid crystal element is single, and when at least one of the first light flux and the second light flux is incident, the emission direction is changed so as to be guided to the corresponding light receiving unit of the photodetector. It is characterized by.

  In addition, in this specification, the light receiving unit outputs a signal for detecting a tracking error of the focused spot with respect to the optical disc track in addition to a signal for detecting a focus error, and also has a function of reading a mark recorded on the optical disc. Of course you may have it.

  The operation of the present invention will be described. FIG. 1 is a schematic diagram of an optical pickup device using a liquid crystal element according to the present invention, and FIG. 2 is a schematic diagram of an optical pickup device that does not use a liquid crystal element according to a comparative example. The light source unit LU, which is a light source, is installed by shifting the first light emitting part LD1 that emits the first light flux with the wavelength λ1 and the second light emitting part LD2 that emits the second light flux with the wavelength λ2 in the direction crossing the optical axis. Yes. In addition, the photodetector PD includes a first light receiving unit that inputs a first light beam having a wavelength λ1 and a second light receiving unit that receives a second light beam having a wavelength λ2.

  First, as indicated by a solid line in FIG. 2, the first light beam having the wavelength λ1 emitted from the first semiconductor laser LD1 passes through the polarization beam splitter PBS, passes through the λ / 4 wavelength plate QWP, and is supplied to the objective optical system OBJ. Thus, the light is condensed on the information recording surface of the first optical disc OD1. The light beam reflected from the information recording surface of the first optical disc OD1 passes through the λ / 4 wavelength plate QWP, is reflected by the polarization beam splitter PBS, and is condensed on the first light receiving portion of the detector PD.

  On the other hand, as indicated by a dotted line in FIG. 2, the second light beam having the wavelength λ2 emitted from the second semiconductor laser LD2 passes through the polarization beam splitter PBS, passes through the λ / 4 wavelength plate QWP, and is supplied to the objective optical system OBJ. Thus, the light is condensed on the information recording surface of the second optical disk OD2. The light beam reflected from the information recording surface of the second optical disk OD2 passes through the λ / 4 wavelength plate QWP, is reflected by the polarization beam splitter PBS, and is condensed on the second light receiving portion of the detector PD.

  Here, since the first light-emitting portion LD1 and the second light-emitting portion LD2 are arranged apart from each other in the direction intersecting the optical axis, the first light-receiving portion and the second light-receiving portion of the photodetector are inherently arranged. By appropriately setting the interval, the first light beam can be incident on the first light receiving unit and the second light beam can be incident on the second light receiving unit. However, when the first light emitting unit LD1 is formed on a chip (hybrid chip) different from the second light emitting unit LD2, the distance Δ between the first light emitting unit LD1 and the second light emitting unit LD2 in the optical axis orthogonal direction Δ. There is a risk of scatter. In such a case, even if the relative position of the light source unit LU and the photodetector PD in the direction perpendicular to the optical axis is set so that the first light beam is incident on the first light receiving unit, the second light beam is incident on the second light receiving unit. Can not be made.

  On the other hand, according to the present invention, the first light beam and the second light beam are passed through the liquid crystal element LCD to change the emission direction, and the first light receiving unit and the second light receiving unit of the photodetector PD appropriately. It can be made to enter. More specifically, in FIG. 1, the liquid crystal element LCD disposed between the polarization beam splitter PBS and the photodetector PD emits light when at least one of the first light beam and the second light beam passing through is incident. The convergence angle or divergence angle of the luminous flux is changed. The light beam reflected from the information recording surface of the first optical disc OD1 passes through the λ / 4 wavelength plate QWP, is reflected by the polarization beam splitter PBS, and is collected in the first light receiving unit via the liquid crystal element LCD and the sensor lens SN. Shine. On the other hand, the light beam reflected from the information recording surface of the second optical disc OD2 passes through the λ / 4 wavelength plate QWP, is reflected by the polarization beam splitter PBS, and passes through the liquid crystal element LCD and the sensor lens SN, thereby passing through the first light receiving unit. The light is condensed on a second light receiving portion different from the above. The liquid crystal element LCD may change the emission direction for only the first light beam, change the emission direction for only the second light beam, or change the emission direction for the first light beam and the second light beam.

  The principle of the liquid crystal element LCD will be described. FIG. 3 is an enlarged view showing the vicinity of the liquid crystal element LCD in the optical pickup device. FIG. 4 is a diagram showing a state in which the liquid crystal element LCD is replaced with an electrically equivalent system.

  In FIG. 3, the liquid crystal element LCD is provided between the first electrode plate E1 installed on the optical disc side (or the photodetector side) and the second electrode plate E2 installed on the photodetector side (or the optical disc side). The liquid crystal portion LC is included. The transparent first electrode plate E1 is grounded to the ground GRD. On the other hand, the second electrode plate E2, which is a high resistance transparent plate, is connected to the high voltage electrode V1 on one side across the optical axis, and the low voltage electrode to which a voltage lower than the high voltage electrode V1 is applied on the other side. Connected to V2. Therefore, as shown in FIG. 4, the second electrode plate E2 has a potential that continuously changes between the electrodes V1 and V2 with respect to the first electrode plate E1, whereby the second electrode plate E2 and the first electrode plate E2 The liquid crystal part LC between the electrode plate E1 is given different voltages in the optical axis orthogonal direction as shown in FIG. 5 (a), and as a result, in the optical axis orthogonal direction as shown in FIG. 5 (b). Different refractive indices will be given. Therefore, the light beam incident on such a liquid crystal element LCD is given a different wavefront phase difference in the direction perpendicular to the optical axis as shown in FIG. 5C, that is, the emission angle azimuth is different from the incident angle azimuth. Will change.

  Here, by adjusting the potential difference between the electrodes V1 and V2, any azimuth change can be given to the emitted light. That is, when θ1 is a change in the exit angle with respect to the incident angle of the first light flux incident on the liquid crystal element LCD and θ2 is a change in the exit angle with respect to the incident angle of the second light flux, the angles θ1 and θ2 are set to desired values ( Both include zero), so that the light can be appropriately incident on the first light receiving unit and the second light receiving unit of the photodetector PD.

  An optical pickup device according to a second aspect is the optical pickup device according to the first aspect, wherein the optical beam pickup device is disposed between the polarizing beam splitter that reflects or transmits the light beam from the light source, and the polarizing beam splitter and the objective lens. The liquid crystal element has polarization dependency and is disposed between the polarizing beam splitter and the objective lens.

  A general optical pickup device includes a polarizing beam splitter that reflects or transmits a light beam from the light source, and a λ / 4 wavelength plate disposed between the polarizing beam splitter and the objective lens. . Here, when the liquid crystal element is disposed between the polarizing beam splitter and the objective lens, even if the emission angle direction changes due to the light beam traveling toward the optical disk entering the liquid crystal element, When the reflected light is incident on the liquid crystal element again, it is emitted in the original direction due to the same action, and there is a problem that the light condensing position on the photodetector cannot be adjusted. Therefore, in the present invention, the polarization dependency of the liquid crystal element is given.

  The principle of the present invention will be described. In general, the refractive index of a liquid crystal element depends on the angular relationship between the orientation of liquid crystal molecules and the plane of polarization of an incident light beam. For this reason, when the voltage applied to the liquid crystal element changes, the orientation direction of the liquid crystal molecules changes and the refractive index also changes. At the same time, if the direction of the polarization plane changes, the refractive index of the light beam incident thereon changes. However, if the direction of the polarization plane is selected in a specific direction, the refractive index does not change even if the orientation changes. Using this polarization dependence, the lens deflection function is not expressed in the outbound path toward the objective, and the function is expressed in the return path in which the polarization plane is rotated 90 ° from the outbound path through the λ / 4 wavelength plate twice. The magnitude can be controlled by the magnitude of the voltage.

  This will be described more specifically. In FIG. 6, the light beam emitted from the semiconductor laser LD1 or LD2 is reflected by the polarization beam splitter PBS, passes through the liquid crystal element LCD, the collimator lens CU, and the λ / 4 wavelength plate QWP, and is optical disc OD1 or by the objective optical system OBJ. It is condensed on the information recording surface of OD2. The light beam reflected from the information recording surface of the optical disc OD1 or OD2 passes through the λ / 4 wavelength plate QWP, the collimator lens CU, and the liquid crystal element LCD, further passes through the polarization beam splitter PBS, and is condensed on the detector PD.

  FIG. 7 shows a refractive index ellipsoid of the liquid crystal element LCD. In the refractive index ellipsoid of FIG. 7, the cross section in the minor axis direction is the ACBD plane, the cross section rotated by a predetermined angle from the ACBD plane is the AEBF plane, and the length of the diagonal line represents the refractive index. Here, in a state where no voltage is applied to the liquid crystal element LCD (see FIG. 8A), the refractive index is expressed on the ACBD surface. That is, the forward light passing through the liquid crystal element LCD passes through because the polarization direction coincides with AB, and the return light passing through the λ / 4 wave plate twice coincides with the polarization direction of CD, but is refracted because AB = CD. The rate does not change (see FIG. 8A), that is, the liquid crystal element LCD is equivalent to the parallel plate for the forward light and the backward light. On the other hand, in a state where a voltage is applied to the liquid crystal element LCD (see FIG. 8B), the refractive index is expressed on the AEBF plane. That is, the forward light passing through the liquid crystal element LCD passes through because the polarization direction coincides with AB, and the return light passing through the λ / 4 wave plate twice coincides with EF, but AB <EF, and is refracted because AB <EF. Since the rate changes, only the return light passing through the liquid crystal element LCD passes through media having different refractive indexes. Using this action, the exit angle direction can be changed by the liquid crystal element LCD with respect to the passing light beam. The change of the emission angle azimuth is executed as shown in FIGS.

  According to a third aspect of the present invention, in the optical pickup device according to the second aspect, the λ / 4 wavelength plate and the liquid crystal element are integrated.

  Various forms of λ / 4 wave plates are known, but one using liquid crystal is an example. Specifically, by applying a voltage to the liquid crystal part sandwiched between a pair of electrode plates, the passing light can be converted from linearly polarized light to circularly polarized light or vice versa, and since this is a known technique, details are described. Is not described.

  Such a λ / 4 wavelength plate is preferably integrated with the liquid crystal element. FIG. 9 shows an element in which a λ / 4 wavelength plate and a liquid crystal element are integrated. In such an element, liquid crystal portions LC and LC ′ are arranged between three electrode plates E1, E2 and E3, and the liquid crystal portion LC between the electrode plates E1 and E2 constitutes the liquid crystal element LCD of FIG. Further, the function of the λ / 4 wavelength plate is exhibited by applying a potential difference V3 to the liquid crystal part LC ′ between the electrode plates E2 and E3. Here, by grounding the center electrode plate E2 to the ground GRD, it is possible to make the ground common, and it is possible to reduce the size and cost.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to the second aspect of the invention, further comprising an aberration correction element that corrects an aberration of a light beam condensed on the optical disc, and the aberration correction element and the liquid crystal element are integrated. It is characterized by that.

  Various forms of aberration correction elements are known, but one example uses liquid crystal. Specifically, one of the electrode plates is divided into a plurality of annular zones, and a different potential difference is given to the other electrode plate, so that the annular zone is applied to the light passing through the liquid crystal unit disposed therebetween. Different spherical aberrations can be given for each, and since it is a known technique, details are not described.

  Such an aberration correction element is preferably integrated with the liquid crystal element. FIG. 10 shows an aberration correction element, and FIG. 11 shows an element in which the aberration correction element and the liquid crystal element are integrated. As shown in FIG. 10A, the electrode E4 includes ring zones RG1 to RG4 divided on four concentric circles, and voltages Va to Vd are applied independently. Here, when different voltages Va to Vd are applied to the ring zones RG1 to RG4 of the electrode E4, the light passing through the liquid crystal portion LC ″ between the electrodes E2 and E4 differs as shown in FIG. 10B. The phase difference is imparted point-symmetrically, so that it is possible to correct the spherical aberration caused by the temperature change and the spherical aberration due to the difference in the cover layer thickness of the plurality of information recording layers. By connecting to the ground GRD, it is possible to make the ground common and to reduce the size and cost.In addition, the shape of the annular zone is arbitrary and gives coma and astigmatism. In addition, three elements of an aberration correction element, a λ / 4 plate element, and a liquid crystal element may be integrated.

  The optical pickup device according to claim 5 is the optical pickup device according to any one of claims 1 to 4, wherein the first light emitting unit is formed on a chip different from the second light emitting unit, and is formed on the support substrate. It is attached.

  The optical pickup device according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the first light receiving unit and the second light receiving unit are common. Thereby, the structure of a photodetector can be simplified.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the light source includes a third light emitting unit that emits a third light flux having a wavelength λ3 (λ2 <λ3). A spot is formed by condensing the light beam from the third light emitting unit on the information recording surface of the third optical disk by the objective optical system, and the reflected light is transmitted through the liquid crystal element to the first light detector. Three light receiving portions are configured to receive light.

  An optical pickup device according to an eighth aspect is the invention according to the seventh aspect, wherein the first light receiving unit and the second light receiving unit are common. Thereby, the structure of a photodetector can be simplified.

The optical pickup device described in claim 9 is characterized in that, in the invention described in claim 7 or 8, the following expression is satisfied.
395 (nm) ≦ λ1 ≦ 415 (nm) (1)
630 (nm) ≦ λ2 ≦ 700 (nm) (2)
750 (nm) ≦ λ3 ≦ 850 (nm) (3)

  According to the present invention, it is possible to provide an optical pickup device capable of appropriately recording / reproducing information on two or more different types of optical discs while reducing the size and reducing the cost.

It is the schematic of the optical pick-up apparatus using the liquid crystal element concerning this invention. It is the schematic of the optical pick-up apparatus which does not use the liquid crystal element concerning a comparative example. It is a figure which expands and shows liquid crystal element LCD vicinity in an optical pick-up apparatus. It is a figure which shows the state which replaced liquid crystal element LCD with the electrically equivalent system. (A) is a figure which shows the relationship between the position (y) between electrode V1, V2 of a liquid crystal element, and an electrical potential difference, (b) is the position (y) between electrode V1, V2 of a liquid crystal element, and refractive index (n (C) is a diagram showing the relationship between the position (y) between the electrodes V1 and V2 of the liquid crystal element and the wavefront phase difference imparted to the emitted light, and blue light and red Each shows about light. It is the schematic of the optical pick-up apparatus using the liquid crystal element concerning another example of this invention. It is a figure which shows the refractive index ellipsoid of liquid crystal element LCD. It is a figure which shows the state from which the function of liquid crystal element LCD differs by outward light and return light. It is a figure which shows the element which integrated the (lambda) / 4 wavelength plate and the liquid crystal element. (A) is a front view of the aberration correction element, and (b) is a diagram schematically showing spherical aberration given by the aberration correction element. It is a figure which shows the element which integrated the aberration correction element and the liquid crystal element. It is the schematic which shows an example of the 3 compatible optical pick-up apparatus which performs the focus detection of the 1st light beam using the beam size method. It is a figure which shows the light-receiving surface in the 1st light-receiving part of photodetector PD with the spot SP. (A) is schematic which shows an example of the 3 compatible optical pick-up apparatus which performs the focus detection of a 1st light beam using a knife edge method, (b) is the diffraction element DE and photodetector PD from a side. FIG. It is a figure which shows the light-receiving surface in the 1st light-receiving part of photodetector PD with the spot SP. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment. It is the figure which looked at the light-receiving surface of photodetector PD shown in FIG. 16 in the arrow XVI direction. It is a figure which shows schematically the structure of optical pick-up apparatus PU2 of another embodiment. It is a figure which shows schematically the structure of optical pick-up apparatus PU3 of another embodiment. It is the figure which looked at the light-receiving surface of photodetector PD shown in FIG. 19 in the arrow XX direction. It is a figure which expands and shows the site | part shown by arrow XXI of optical pick-up apparatus PU3 shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As a method for detecting a focus error signal, there are a beam size method and a knife edge method. These will be specifically described.

  FIG. 12 is a schematic diagram showing an example of a 3-compatible optical pickup device that performs focus detection of the first light beam using the beam size method. FIG. 13 is a diagram illustrating a light receiving surface of the first light receiving unit of the photodetector PD together with a spot SP. In FIG. 12, the second and third semiconductor lasers are omitted. The first semiconductor laser LD1 that emits the first light flux is bonded to the support substrate HP together with the second and third semiconductor lasers (not shown), and the direction of the bonding surface is the x direction (vertical direction in the figure). And At this time, the direction corresponding to the x direction on the photodetector PD is defined as the x ′ direction. That is, when the first semiconductor laser LD1 is shifted in the x direction, the spot focused on the photodetector PD is shifted in the x 'direction.

  The photodetector PD has two first light receiving portions (A, B) for receiving the first light flux. As shown in FIG. 13, each first light receiving unit has two dividing lines DL extending in the x ′ direction, whereby the light receiving surface has three regions (A1 to A3, B1 to B3), respectively. The signals to be output are respectively A1 signal, A2 signal, A3 signal, B1 signal, B2 signal, and B3 signal. The diffractive element DE having the diffractive structure DS receives + N-order diffracted light and −M-order diffracted light (N and M are natural numbers other than 0) as diffracted light having the highest diffraction efficiency when a light beam having a wavelength λ1 is incident, x ′ Occurs to split in the direction. The + Nth order diffracted light is condensed before the light receiving surface of the photodetector PD, that is, given a condensing action, and the −Mth order diffracted light is condensed behind the light receiving surface of the photodetector PD, that is, has a diverging action. Given. Such a diffractive structure DS is disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-174503.

  Here, the convergent light traveling toward the photodetector PD is divided into two C-shapes when viewed from the side by the diffractive structure DS of the diffractive element DE, and each of the two convergent lights has a focal point in the optical axis direction. To be different. Specifically, the converging light focused on the light receiving part A has a focal point in front of it, and the converging light condensed on the light receiving part B has a focal point on the far side. When the light beam having the wavelength λ1 collected by the objective optical system is in a focused state with respect to the information recording surface of the BD, both spot sizes in the light receiving portions A and B are the same, and the center of each of the three divided light receiving regions. Adjusted so that it hits. At this time, the outputs from the light receiving portions A and B are both zero, that is, the spot size and the position of the dividing line DL are set so that the signals of the regions on both sides = the center signal. This may be performed by injecting an electrical offset k such that (both side signals−center signal−k) = 0.

  In the case of this example, if the objective optical lens OBJ moves away from the BD, for example, the spot size increases on the light receiving part A and decreases on the light receiving part B, so the signals from the two light receiving parts A and B are Since the outputs are substantially the same and have opposite polarities, these differential signals can be used as the final FE signal. Thereby, optical and electrical noise other than the focus error can be canceled. Here, there is also an advantage that the light emitting point position deviation of the first semiconductor laser can be adjusted regardless of whether it is positive or negative in the z direction.

  The light beam having the wavelength λ1 emitted from the first semiconductor laser LD1 is reflected by the polarization beam splitter PBS, passes through the λ / 4 wavelength plate QWP, and is condensed on the information recording surface of the BD by the objective optical system OBJ. The light beam reflected from the information recording surface of the BD passes through the λ / 4 wave plate QWP and the polarization beam splitter, and further passes through the diffraction element DE to generate + Nth order diffracted light and −Mth order diffracted light, and the photodetector PD. The spots SP are formed on the two regions A and B, respectively. At this time, a focus error signal (FE signal) can be formed using the signal output from the photodetector PD.

  More specifically, the spot SP formed on the photodetector PD is at the far side defocus (FIG. 13 (a)), at the time of focusing (FIG. 13 (b)), and at the near side defocus (FIG. 13). 13 (c)), the spot diameter gradually changes in the opposite direction at the light receiving portions A and B. That is, since the signal ratio output from the three divided regions (A1 to A3, B1 to B3) changes according to the defocus state, if FE = (A1 + A3 + B2) − (B1 + B3 + A2) is calculated as the FE signal, When this becomes a predetermined value (for example, 0), it can be determined that the in-focus state.

  Here, if the position of the first semiconductor laser LD1 in the x direction is shifted from the position of the photodetector PD in the x 'direction, the focus detection signal cannot be obtained with high accuracy. Therefore, a voltage is applied to the liquid crystal element LCD to change the direction of the outgoing light with respect to the incident light, and the spots SP1 and SP2 can be appropriately condensed on the light receiving portion of the photodetector PD. The same applies to the second and third semiconductor lasers, but the description is omitted here.

  Next, the knife edge method will be described. FIG. 14A is a schematic diagram showing an example of a three-compatible optical pickup device that performs focus detection of the first light beam using the knife edge method, and FIG. 14B shows a diffraction element DE and a photodetector PD. It is the figure which looked at from the side. FIG. 15 is a diagram illustrating the light receiving surface of the first light receiving unit of the photodetector PD together with the spots SP1 and SP2. In FIG. 14, the second and third semiconductor lasers are omitted. The first semiconductor laser LD1 that emits the first light flux is bonded to the support substrate HP together with the second and third semiconductor lasers (not shown), and the direction of the bonding surface is the x direction (vertical direction in the figure). And At this time, the direction corresponding to the x direction on the photodetector PD is defined as the x ′ direction. That is, when the first semiconductor laser LD1 is shifted in the x direction, the spot focused on the photodetector PD is shifted in the x 'direction.

  The light detector PD has a first light receiving portion including two light receiving surfaces (A, B) arranged in the x ′ direction in order to receive the first light flux. As shown in FIG. 15, each first light receiving unit has one dividing line DL extending in the x ′ direction, so that each light receiving surface has two regions (A1, A2, B1, B2). The signals to be output are respectively A1 signal, A2 signal, B1 signal, and B2 signal. The diffractive element DE having the diffractive structure DS generates ± Nth order diffracted light (N is an integer other than 0) as diffracted light having the highest diffraction efficiency when a light beam having a wavelength λ1 is incident.

  Here, the convergent light traveling toward the photodetector PD is divided into two C-shapes when viewed from the side by the diffraction structure DS of the diffractive element DE, and the two convergent lights have polarities in a holographic element (not shown) or the like. By passing different regions, the side on which the semicircle is formed is reversed. However, unlike the beam size method, it is assumed that the focal positions of the two convergent lights toward the light receiving portions A and B are in the same plane with respect to the direction perpendicular to the optical axis.

  In the case of this example, if the objective optical system OBJ approaches the optical disc OD1, for example, a spot SP is generated on the region A1 side of the light receiving unit A and the region B2 side of the light receiving unit B, and from the two light receiving units A1 and B2. Assuming that the signals have substantially the same output, and the distance from the objective optical system, a spot SP is generated on the region A2 side of the light receiving unit A and on the region B1 side of the light receiving unit B, and from the two light receiving units A2 and B1. Since these signals have substantially the same output, these differential signals can be used as final FE signals. Thereby, optical and electrical noise other than the focus error can be canceled.

  In FIG. 14, the light beam having the wavelength λ1 emitted from the first semiconductor laser LD1 is reflected by the polarization beam splitter PBS, passes through the λ / 4 wavelength plate QWP, and is collected on the information recording surface of the optical disk OD1 by the objective optical system OBJ. To be lighted. The light beam reflected from the information recording surface of the optical disk OD1 passes through the λ / 4 wave plate QWP and the polarization beam splitter, and further passes through the liquid crystal element LCD and the diffraction element DE to generate ± Nth order diffracted light. Spots SP are formed on the two regions A and B of the PD, respectively. At this time, a focus error signal (FE signal) can be formed using the signal output from the photodetector PD.

  More specifically, the semicircular spot SP formed on the photodetector PD is defocused at the far side defocus (FIG. 15 (a)), focused (FIG. 15 (b)), and near side defocused. The spot diameter gradually changes at the light receiving portions A and B (FIG. 15C). That is, since the signal ratio output from each of the two divided areas (A1, A2, B1, B2) changes according to the defocus state, if FE = (A1 + B2) − (A2 + B1) is calculated as the FE signal. The time when this becomes a predetermined value (for example, 0) can be determined to be in focus.

  Here, if the position of the first semiconductor laser LD1 in the x direction is shifted from the position of the photodetector PD in the x 'direction, the focus detection signal cannot be obtained with high accuracy. Therefore, a voltage is applied to the liquid crystal element LCD to change the direction of the outgoing light with respect to the incident light, and the spots SP1 and SP2 can be appropriately condensed on the light receiving portion of the photodetector PD. The same applies to the second and third semiconductor lasers, but the description is omitted here.

  FIG. 16 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. FIG. 17 is a view of the light receiving surface of the photodetector PD shown in FIG. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes a single objective lens OBJ as an objective optical system, a λ / 4 wavelength plate QWP, a spherical aberration correction element CU1 movable in the optical axis direction, a fixed collimator lens CU2, and a light beam separation element. A first semiconductor laser LD1 (first light-emitting unit) that emits a laser beam (first beam) having a wavelength λ1 = 405 nm and is emitted when information is recorded / reproduced with respect to the polarization beam splitters PBS and BD; On the other hand, when recording / reproducing information, a second semiconductor laser LD2 (second light-emitting unit) that emits a laser beam (second beam) emitted at a wavelength of λ2 = 655 nm and information recording / reproduction with respect to a CD. Is integrated with a third semiconductor laser LD3 (third light emitting unit) that emits a laser beam (third beam) having a wavelength λ3 = 785 nm. Having accommodating the light source unit LDP, grating GRT to 3 divided and emits the incident light beam, the sensor lens SN, similar liquid crystal device LCD as shown in FIG. 3, a photodetector PD, and the like. The second semiconductor laser LD2 and the third semiconductor laser LD3 are formed on the same chip of the Ga-based semiconductor substrate (monolithic configuration), and the first semiconductor laser LD1 is formed on a chip of a different nitride-based semiconductor substrate. Yes (hybrid configuration). An example of such a light source is disclosed in Japanese Patent Application Laid-Open No. 2004-319915.

  As shown in FIG. 17, the photodetector PD includes light receiving portions 11R to 33R arranged in 3 rows and 3 columns on the light receiving surface side substantially orthogonal to the optical axis. The light receiving portions 11R to 13R are first light receiving portions that receive the reflected light from the BD, the light receiving portions 21R to 23R are second light receiving portions that receive the reflected light from the DVD, and the light receiving portions 31R to 33R are from the CD. Is a third light-receiving unit that receives the reflected light, and outputs a signal corresponding to the amount of light received. The light receiving unit 12R is divided into four parts in the vertical and horizontal directions, and the received light amounts are 1e, 1c, 1f, and 1d, respectively. The light receiving portions 11R and 13R on both sides of the light receiving portion 12R are divided into left and right parts, and the received light amounts are 1h, 1g, and 1b, 1a, respectively. The light receiving unit 22R is divided into four parts, top, bottom, left, and right, and the amounts of light received are 2e, 2c, 2f, and 2d, respectively. The light receiving parts 21R and 23R on both sides of the light receiving part 22R are divided into left and right parts, and the received light amounts are 2h, 2g, 2b and 2a, respectively. Further, the light receiving unit 32R is divided into four parts in the vertical and horizontal directions, and the received light amounts are 3e, 3c, 3f, and 3d, respectively. The light receiving portions 31R and 33R on both sides of the light receiving portion 32R are divided into left and right parts, and the received light amounts are 3h, 3g, 3b, and 3a, respectively.

  When the optical pickup device PU1 is assembled, the voltage applied to the liquid crystal element LCD is set to zero, the first semiconductor laser LD1 of the fixed light source unit LDP is caused to emit light, and the light receiving units 11R to 13R of the photodetector PD receive light appropriately. The position is adjusted to fix the photodetector PD. Next, the second semiconductor laser LD2 of the light source unit LDP is caused to emit light, and a voltage is applied to the liquid crystal element LCD so that the light is received by the light receiving portions 21R to 23R of the fixed photodetector PD, thereby adjusting the direction of emitted light. And store the voltage as V (R). Furthermore, the direction of the emitted light is adjusted by applying a voltage to the liquid crystal element LCD so that the third semiconductor laser LD3 of the light source unit LDP emits light and appropriately receives light at the light receiving portions 31R to 33R of the fixed photodetector PD. And store the voltage as V (IR). It should be noted that by utilizing the fact that the refractive index of the liquid crystal changes according to the wavelength, the voltage applied to the liquid crystal element LCD may be made constant so that the light beams of the respective wavelengths are received by the respective light receiving portions. .

  Next, the operation of the optical pickup device PU1 will be described. When the BD is used, no voltage is applied to the liquid crystal element LCD. The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the first semiconductor laser LD1 passes through the grating GRT and is divided into three, as shown by the solid line, and then reflected by the polarization beam splitter PBS, and then collimator lens A light beam that passes through CU2 and spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by a λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the light beam collected by the objective lens OBJ is The spots are formed on the information recording surface of the BD through a protective substrate having a thickness of 0.1 mm.

  The reflected light beam modulated by the information pits on the information recording surface of the BD again passes through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam which has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarization beam splitter PBS, the sensor lens SN and the liquid crystal element LCD is divided into three on the light receiving portions 11R to 13R of the photodetector PD. Converge to. Then, the information recorded on the BD can be read by using the output signal of the photodetector PD to focus or track the objective lens OBJ by an objective lens actuator (not shown).

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the BD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (1c + 1f) − (1e + 1d), and the objective lens OBJ is focused by the objective lens actuator so that the FE signal approaches zero.

  On the other hand, the tracking servo uses the DPP method. In the DPP method, the TE signal is obtained by (1a + 1g + 1e + 1f) − (1b + 1h + 1c + 1d), and the objective lens OBJ is tracked by the objective lens actuator so that the TE signal approaches zero. The RF signal is the sum of the amounts of received light, and is represented by (1a + 1b + 1c + 1d + 1e + 1f + 1g + 1h).

  Next, when the DVD is used, the voltage V (R) is applied to the liquid crystal element LCD. The divergent light beam of the second light beam (λ2 = 655 nm) emitted from the second semiconductor laser LD2 passes through the grating GRT and is divided into three, as indicated by the alternate long and short dash line, and then reflected by the polarization beam splitter PBS, and is collimated. A light beam that passes through the lens CU2 and the spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and further collected by the objective lens OBJ. Are spots formed on the information recording surface of the DVD through a protective substrate having a thickness of 0.6 mm.

  The reflected light beam modulated by the information pits on the information recording surface of the DVD is again transmitted through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam that has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarization beam splitter PBS, the sensor lens SN, and the liquid crystal element LCD is divided into three light beams on the light receiving portions 21R-23R of the photodetector PD. Converge to. Then, using the output signal of the photodetector PD, the objective lens OBJ is focused and tracked by an unillustrated objective lens actuator, whereby the information recorded on the DVD can be read.

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the DVD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (2c + 2f) − (2e + 2d), and the objective lens OBJ is focused by the objective lens actuator so that this becomes close to zero.

  On the other hand, the tracking servo uses the DPP method. In the DPP method, the TE signal is obtained by (2a + 2g + 2e + 2f) − (2b + 2h + 2c + 2d), and the objective lens OBJ is tracked by the objective lens actuator so that the TE signal approaches zero. The RF signal is the sum of the amounts of received light, and is represented by (2a + 2b + 2c + 2d + 2e + 2f + 2g + 2h).

  Next, when the CD is used, a voltage V (IR) is applied to the liquid crystal element LCD. The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the third semiconductor laser LD3 passes through the grating GRT and is divided into three, as shown by the dotted line, and then is reflected by the polarization beam splitter PBS to be collimator lenses. A light beam that passes through CU2 and spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by a λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the light beam collected by the objective lens OBJ is The spots are formed on the information recording surface of the CD through a protective substrate having a thickness of 1.2 mm.

  The reflected light beam modulated by the information pits on the information recording surface of the CD is again transmitted through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam that has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarizing beam splitter PBS, the sensor lens SN, and the liquid crystal element LCD is divided into three light beams on the light receiving portions 31R to 33R of the photodetector PD. Converge to. Then, using the output signal of the photodetector PD, the objective lens OBJ is focused or tracked by an unillustrated objective lens actuator, whereby the information recorded on the CD can be read.

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the CD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (3c + 3f) − (3e + 3d), and the objective lens OBJ is focused by the objective lens actuator so that this becomes close to zero.

  On the other hand, the tracking servo uses the DPP method. In the DPP method, the TE signal is obtained by (3a + 3g + 3e + 3f) − (3b + 3h + 3c + 3d), and the objective lens OBJ is tracked by the objective lens actuator so that this approaches zero. The RF signal is the sum of the amounts of received light, and is represented by (3a + 3b + 3c + 3d + 3e + 3f + 3g + 3h).

  Since the second semiconductor laser LD2 and the third semiconductor laser LD3 are formed on the same chip, and the first semiconductor laser LD1 is formed on a different chip, the first semiconductor laser LD1 and the first semiconductor laser LD1 are combined with the light source unit LDP. The gap between the second semiconductor laser LD2 and the third semiconductor laser LD3 varies. On the other hand, the relative positions of the light receiving portions 11R to 33R of the photodetector PD cannot be shifted. Therefore, when the interval between the semiconductor lasers exceeds the allowable error, each light beam cannot be properly received by the light receiving portions 11R to 33R. Therefore, in the present embodiment, by driving the liquid crystal element LCD and changing the direction of the outgoing light beam with respect to the incident light beam as described with reference to FIG. 3, any light beam can be appropriately directed to each light receiving unit. become.

  FIG. 18 is a schematic view of an optical pickup device PU2 in which the liquid crystal element LCD is disposed between the light source unit LDP and the polarization beam splitter PBS instead of being disposed between the photodetector PD and the polarization beam splitter PBS. . The rest is the same as the embodiment shown in FIG. The liquid crystal element LCD having the function shown in FIGS. 7 and 8 may be disposed between the objective lens OBJ and the polarization beam splitter PBS. Further, the liquid crystal element LCD may be applied to a two-compatible optical pickup device.

  FIG. 19 is a diagram schematically showing a configuration of an optical pickup device PU3 of still another embodiment capable of appropriately recording and / or reproducing information on BD, DVD and CD which are different optical disks. It is. FIG. 20 is a view of the light receiving surface of the photodetector PD shown in FIG. 19 as viewed in the direction of arrow XX. FIG. 21 is an enlarged view showing a portion indicated by an arrow XXI of the optical pickup device PU3 shown in FIG. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes a single objective lens OBJ as an objective optical system, a λ / 4 wavelength plate QWP, a spherical aberration correction element CU1 that can move in the optical axis direction, a fixed collimator lens CU2, and a light beam separation element. A first semiconductor laser LD1 (first light emitting unit) that emits a laser beam (first beam) having a wavelength λ1 = 405 nm, which is emitted when information is recorded / reproduced with respect to the polarization beam splitters PBS and BD, and a DVD A second semiconductor laser LD2 (second light-emitting unit) that emits a laser beam (second beam) having a wavelength of λ2 = 655 nm and records / reproduces information to / from a CD. A third semiconductor laser LD3 (third light emitting unit) that emits a laser beam (third beam) emitted at the time of reproduction and having a wavelength λ3 = 785 nm is integrated into one package. A light source unit LDP, which contains di, grating GRT to 3 divided and emits the incident light beam, the sensor lens SN, similar liquid crystal device LCD as shown in FIG. 3, a photodetector PD, and the like. The second semiconductor laser LD2 and the third semiconductor laser LD3 are formed on the same chip of the Ga-based semiconductor substrate (monolithic configuration), and the first semiconductor laser LD1 is formed on a chip of a different nitride-based semiconductor substrate. Yes (hybrid configuration).

  As shown in FIG. 20, the photodetector PD includes three light receiving portions 1R to 3R arranged on the light receiving surface side substantially orthogonal to the optical axis. The light receiving units 1R to 3R are light receiving units that receive reflected light from the BD, DVD, and CD in common, and output a signal corresponding to the amount of received light. That is, the first light receiving unit, the second light receiving unit, and the third light receiving unit are common examples. The light receiving unit 2R is divided into four parts, up, down, left, and right, and the received light amounts are e, c, f, and d, respectively. The light receiving portions 1R and 3R on both sides of the light receiving portion 2R are not divided, and the amounts of received light are b and a, respectively.

  When the optical pickup device PU1 is assembled, the voltage applied to the liquid crystal element LCD is set to zero, the first semiconductor laser LD1 of the fixed light source unit LDP is caused to emit light, and the light receiving units 1R to 3R of the photodetector PD receive light appropriately. The position is adjusted to fix the photodetector PD. Next, a predetermined voltage is applied to the liquid crystal element LCD so that the second semiconductor laser LD2 of the light source unit LDP emits light and is appropriately received by the light receiving portions 1R to 3R of the fixed photodetector PD, and the direction of the emitted light Make adjustments and store the voltage as V (R). Furthermore, the direction of the emitted light is adjusted by applying a voltage to the liquid crystal element LCD so that the third semiconductor laser LD3 of the light source unit LDP emits light and appropriately receives light at the light receiving portions 31R to 33R of the fixed photodetector PD. And store the voltage as V (IR). It should be noted that by utilizing the fact that the refractive index of the liquid crystal changes according to the wavelength, the voltage applied to the liquid crystal element LCD may be made constant so that the light beams of the respective wavelengths are received by the respective light receiving portions. .

  Next, the operation of the optical pickup device PU1 will be described. When the BD is used, no voltage is applied to the liquid crystal element LCD. The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the first semiconductor laser LD1 passes through the grating GRT and is divided into three, as shown by the solid line, and then reflected by the polarization beam splitter PBS, and then collimator lens A light beam that passes through CU2 and spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by a λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the light beam collected by the objective lens OBJ is The spots are formed on the information recording surface of the BD through a protective substrate having a thickness of 0.1 mm. Incidentally, a spot formed on the information recording surface of the BD, a spot formed on the information recording surface of the DVD described later, and a spot formed on the information recording surface of the CD are mutually in the thickness direction of the optical disk and It is shifted in the direction perpendicular to it.

  The reflected light beam modulated by the information pits on the information recording surface of the BD again passes through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam that has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarizing beam splitter PBS, the sensor lens SN, and the liquid crystal element LCD is divided into three light beams on the light receiving portions 1R to 3R of the photodetector PD. Converge to. Then, the information recorded on the BD can be read by using the output signal of the photodetector PD to focus or track the objective lens OBJ by an objective lens actuator (not shown).

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the BD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (c + 1) − (e + d), and the objective lens OBJ is focused by the objective lens actuator so that this becomes close to zero.

  On the other hand, the tracking servo uses a three-beam method. In the three-beam method, the TE signal is obtained by (ab), and the objective lens OBJ is tracked by the objective lens actuator so that the TE signal approaches zero. The RF signal is the sum of the amounts of received light and is represented by (a + b + c + d + e + f).

  The reflected light of any wavelength from the optical disk matches with the objective lens OBJ. However, as shown in FIG. 21, the first light beam, the second light beam, and the third light beam are subsequently shifted from each other, and the liquid crystal element With the LCD, the second light beam and the third light beam are changed in direction with reference to the first light beam, thereby converging in common on the light receiving portions 1R to 3R of the photodetector PD. The three light beams incident on the light receiving unit 2R are separated from the four-divided center in a form that is approximately proportional to the wavelength.

  Next, when the DVD is used, the voltage V (R) is applied to the liquid crystal element LCD. The divergent light beam of the second light beam (λ2 = 655 nm) emitted from the second semiconductor laser LD2 passes through the grating GRT and is divided into three, as indicated by the alternate long and short dash line, and then reflected by the polarization beam splitter PBS, and is collimated. A light beam that passes through the lens CU2 and the spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and further collected by the objective lens OBJ. Are spots formed on the information recording surface of the DVD through a protective substrate having a thickness of 0.6 mm.

  The reflected light beam modulated by the information pits on the information recording surface of the DVD is again transmitted through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam that has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarization beam splitter PBS, the sensor lens SN, and the liquid crystal element LCD is divided into three light beams on the light receiving portions 21R-23R of the photodetector PD. Converge to. Then, using the output signal of the photodetector PD, the objective lens OBJ is focused and tracked by an unillustrated objective lens actuator, whereby the information recorded on the DVD can be read.

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the DVD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (c + 1) − (e + d), and the objective lens OBJ is focused by the objective lens actuator so that this becomes close to zero.

  On the other hand, the tracking servo uses a three-beam method. In the three-beam method, the TE signal is obtained by (ab), and the objective lens OBJ is tracked by the objective lens actuator so that the TE signal approaches zero. The RF signal is the sum of the amounts of received light and is represented by (a + b + c + d + e + f).

  Next, when the CD is used, a voltage V (IR) is applied to the liquid crystal element LCD. The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the third semiconductor laser LD3 passes through the grating GRT and is divided into three, as shown by the dotted line, and then is reflected by the polarization beam splitter PBS to be collimator lenses. A light beam that passes through CU2 and spherical aberration correction element CU1, is converted from linearly polarized light to circularly polarized light by a λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the light beam collected by the objective lens OBJ is The spots are formed on the information recording surface of the CD through a protective substrate having a thickness of 1.2 mm.

  The reflected light beam modulated by the information pits on the information recording surface of the CD is again transmitted through the objective lens OBJ and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, thereby correcting spherical aberration. The light beam that has passed through the element CU1 and is converged by the collimator lens CU2 and passes through the polarizing beam splitter PBS, the sensor lens SN, and the liquid crystal element LCD is divided into three light beams on the light receiving portions 31R to 33R of the photodetector PD. Converge to. Then, using the output signal of the photodetector PD, the objective lens OBJ is focused or tracked by an unillustrated objective lens actuator, whereby the information recorded on the CD can be read.

  More specifically, a focus error (FE) signal, a tracking error (TE) signal, and a recording mark reproduction signal (RF) in a state where the focus servo is applied to the BD are observed. As an example, the astigmatism method is used for the focus servo, and the FE signal is obtained by (c + 1) − (e + d), and the objective lens OBJ is focused by the objective lens actuator so that this becomes close to zero.

  On the other hand, the tracking servo uses a three-beam method. In the three-beam method, the TE signal is obtained by (ab), and the objective lens OBJ is tracked by the objective lens actuator so that the TE signal approaches zero. The RF signal is the sum of the amounts of received light and is represented by (a + b + c + d + e + f).

  Since the second semiconductor laser LD2 and the third semiconductor laser LD3 are formed on the same chip, and the first semiconductor laser LD1 is formed on a different chip, the first semiconductor laser LD1 and the first semiconductor laser LD1 are combined with the light source unit LDP. The gap between the second semiconductor laser LD2 and the third semiconductor laser LD3 varies. On the other hand, the relative positions of the light receiving portions 1R to 3R of the photodetector PD cannot be shifted. Therefore, if the distance between the semiconductor lasers exceeds the allowable error, the light beams cannot be appropriately received by the light receiving units 1R to 3R. Therefore, in the present embodiment, by driving the liquid crystal element LCD and changing the direction of the outgoing light beam with respect to the incident light beam as described with reference to FIG. 3, any light beam can be appropriately directed to each light receiving unit. become.

CU1 Spherical aberration correction element CU, CU2 Collimator lens GRT Grating HP Support substrate LCD Liquid crystal element LD1 First semiconductor laser LD2 Second semiconductor laser LD3 Third semiconductor laser LDP Light source unit OBJ Objective lens PBS Polarizing beam splitter PD Photodetectors PU1, PU2 , PU3 Optical pickup device QWP λ / 4 wave plate

Claims (9)

A single light source including a first light emitting unit that emits a first light beam having a wavelength λ1 and a second light emitting unit that emits a second light beam having a wavelength λ2 (λ1 <λ2), an objective optical system, and light detection A spot is formed by condensing the light beam from the first light emitting unit on the information recording surface of the first optical disk by the objective optical system, and the reflected light is reflected on the liquid crystal. The light is received by the photodetector through an element, information is recorded and / or reproduced on the first optical disk based on a signal from the photodetector, and the light beam from the second light emitting unit is A spot is formed by condensing on the information recording surface of the second optical disk by the objective optical system, and the reflected light is received by the photodetector through the liquid crystal element, and based on the signal from the photodetector. Recording and / or information on the second optical disc In the optical pickup device that performs live,
The photodetector includes a first light receiving unit that receives the first light beam, and a second light receiving unit that receives the second light beam,
The liquid crystal element is single, and when at least one of the first light flux and the second light flux is incident, the emission direction is changed so as to be guided to the corresponding light receiving unit of the photodetector. An optical pickup device.   A polarizing beam splitter that reflects or transmits a light beam from the light source; and a λ / 4 wave plate disposed between the polarizing beam splitter and the objective lens. The liquid crystal element has polarization dependency. The optical pickup device according to claim 1, wherein the optical pickup device is disposed between the polarizing beam splitter and the objective lens.   The optical pickup device according to claim 2, wherein the λ / 4 wavelength plate and the liquid crystal element are integrated.   The optical pickup device according to claim 2, further comprising an aberration correction element that corrects an aberration of a light beam condensed on the optical disc, wherein the aberration correction element and the liquid crystal element are integrated.   5. The optical pickup device according to claim 1, wherein the first light emitting unit is formed on a chip different from the second light emitting unit and is attached to the support substrate.   6. The optical pickup device according to claim 1, wherein the first light receiving unit and the second light receiving unit are common.   The light source includes a third light emitting unit that emits a third light beam having a wavelength λ3 (λ2 <λ3), and condenses the light beam from the third light emitting unit on the information recording surface of the third optical disk by the objective optical system. 7. The method according to claim 1, wherein a spot is formed by causing the third light receiving portion of the photodetector to receive the reflected light through the liquid crystal element. The optical pickup device described.   The optical pickup device according to claim 7, wherein the first light receiving unit, the second light receiving unit, and the third light receiving unit are common. The optical pickup device according to claim 7 or 8, wherein the following expression is satisfied.
395 (nm) ≦ λ1 ≦ 415 (nm) (1)
630 (nm) ≦ λ2 ≦ 700 (nm) (2)
750 (nm) ≦ λ3 ≦ 850 (nm) (3)

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