JP2006318553A

JP2006318553A - Optical pickup device

Info

Publication number: JP2006318553A
Application number: JP2005138895A
Authority: JP
Inventors: Seino Ikenaka; Riyuuji Kurokama; Katsuya Yagi; 克哉八木; 清乃池中; 龍司黒釜
Original assignee: Konica Minolta Opto Inc; コニカミノルタオプト株式会社
Priority date: 2005-05-11
Filing date: 2005-05-11
Publication date: 2006-11-24

Abstract

【Task】
Provided is an optical pickup device capable of recording and / or reproducing information in a manner compatible with at least three types of optical information recording media by using a common objective lens and a common photodetector.
[Solution]
The coupling lens COL has a two-group, three-element configuration, and the air interval of each group is variable as will be described later. Therefore, by changing the air interval, each of the semiconductor lasers LD1 to LD3 is changed. By changing the divergence angle according to the wavelength of the emitted light beam and the thickness of the protective substrate of the optical disk, it is possible to form an appropriate condensing spot on the information recording surfaces of the optical disks OD to OD3.
[Selection] Figure 3

Description

The present invention relates to an optical pickup device, and more particularly to an optical pickup device capable of appropriately recording and / or reproducing information with respect to an optical information recording medium.

In recent years, research and development of a high-density optical disk system capable of recording / reproducing information using a blue-violet semiconductor laser having a wavelength of about 400 nm is rapidly progressing. As an example, an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (BD), is the same size as DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB). On an optical disk with a diameter of 12 cm, information of 20 to 30 GB can be recorded on one surface, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called HD DVD In addition, it is possible to record information of 15 to 20 GB per side on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, such an optical disc is referred to as a “high density DVD”.

By the way, it cannot be said that the value as a product of the optical pickup device is sufficient only by being able to appropriately record / reproduce information on such a high-density DVD. In light of the fact that DVDs and CDs that record a wide variety of information are currently being sold, it is not only possible to record / reproduce information appropriately for high-density DVDs. For example, conventional DVDs owned by users Alternatively, it is possible to record / reproduce information appropriately for a CD as well, which leads to an increase in the value of a product as a compatible type optical pickup device. From such a background, the optical system used for the compatible type optical pickup device has, of course, a low-cost and simple configuration, and in addition to high-density DVDs, conventional DVDs, and CDs, It is desired to obtain a good spot in order to properly record / reproduce information. In addition, an optical pickup device capable of recording and / or reproducing information in a manner compatible with DVD and CD has been put into practical use, but further downsizing, thinning, and cost reduction with respect to the current configuration. Etc. are desired.

Patent Documents 1 and 2 disclose information on two different types of optical disks using a movable coupling lens while realizing a compact configuration by using a common objective lens and a common photodetector. An optical pickup device capable of recording and / or reproducing is disclosed.
JP-A-10-199021 JP 2002-236253 A

However, the optical pickup devices disclosed in Patent Documents 1 and 2 perform recording and / or reproduction of information on two different types of optical discs, and on at least three types of optical discs including high-density optical discs. Thus, when recording and / or reproducing information, further ingenuity is required.

The present invention has been made in view of such problems of the prior art, and is compatible with at least three types of optical information recording media using a common objective lens and a common photodetector. It is an object of the present invention to provide an optical pickup device capable of recording and / or reproducing.

The optical pickup device according to claim 1, a first light source that emits a light beam with a wavelength λ1 of 390 to 420 nm, a second light source that emits a light beam with a wavelength λ2 of 630 to 670 nm, and a wavelength of 760 to 800 nm. A third light source that emits a light beam of λ3, an objective lens that condenses the light beam from the light source on the information recording surface of the optical information recording medium, and the first, second, and third light sources. The coupling lens disposed in the optical path of the light source and the objective lens and the light beam reflected from the information recording surface of the optical information recording medium are separated from the light beam from the light source. A light beam separating unit, and a light receiving element that receives the light beam separated from the information recording surface of the optical information recording medium and separated by the light beam separating unit,
The coupling lens is composed of two or more lenses in two groups, and at least one group of the constituting lenses is arranged to be movable in the optical axis direction.
A light receiving unit for receiving the light beam emitted from the first light source, the light beam emitted from the second light source, and the light beam emitted from the third light source is provided in one light receiving element. Packaged,
The light beam emitted from the first light source, the light beam emitted from the second light source, and the light beam emitted from the third light source reflected from the information recording surface of the optical information recording medium are common. Is received by the light receiving portion of the light receiving element through the optical element,
The luminous flux emitted from the first light source is incident on the objective lens after being given a first divergence angle (θ1) by the coupling lens in which the at least one group has moved to the first position. The information is recorded and / or reproduced by being condensed on the information recording surface of the first information recording medium having the recording density ρ1,
The luminous flux emitted from the second light source is given a second divergence angle (θ2) by the coupling lens in which the at least one group has moved to the second position, and then recorded by the objective lens. Information is recorded and / or reproduced by being condensed on the information recording surface of the second information recording medium having a density ρ2 (ρ1> ρ2).
The light beam emitted from the third light source is given a third divergence angle (θ3) by the coupling lens in which the at least one group has moved to the third position, and then recorded by the objective lens. Information is recorded and / or reproduced by being condensed on the information recording surface of the third information recording medium having a density ρ3 (ρ2> ρ3).
The three light sources and the light receiving portion of the light receiving element are optically conjugate with each other via an information recording surface of each optical information recording medium.

In this specification, the “divergence angle” includes a case where the emission angle is zero or negative, that is, a case where at least one light beam is incident on the objective lens in the state of infinite parallel light or convergent light.

In order to record and / or reproduce information on at least three types of optical information recording media (also referred to as optical discs) using a common objective lens and a common photodetector, three light sources and an objective focus are used. It is desirable that the light receiving surface of the light receiving element that is the photodetector is in an optically conjugate positional relationship. The reason will be described.

First, in order to obtain a good imaging spot on the information recording surface of the optical disc for each of the three wavelengths, it can be said that the spherical aberration caused by the thickness of the protective substrate of the disc must be corrected with the wavelength difference and the light. is there. For example, in a conventional optical pickup device capable of recording and / or reproducing information in a manner compatible with DVD / CD, the spherical aberration is corrected by an optical element other than the objective lens or by the entire optical pickup device. In this case, it is desirable that the divergence angle (or convergence angle or parallelism) of the light beam incident on the objective lens is individually set to a predetermined value. One example will be described.

FIG. 1 is a schematic diagram of an optical pickup device as a comparative example in which three light sources having different wavelengths are arranged at positions where light beams incident on an objective lens each have a predetermined divergence angle. FIG. 2 is a diagram showing a positional relationship between each light source and each light receiving element when information is recorded and / or reproduced on each optical disc.

For example, for the short wavelength light source LD1, a long distance between the light source LD1 and the objective lens OBJ is secured (FIG. 2C), and for the long wavelength light source LD3, a short distance between the light source LD3 and the objective lens OBJ is secured. However, with respect to the light source LD2 having an intermediate wavelength, the distance between the light source LD2 and the objective lens OBJ is ensured in the middle (FIG. 2B), so that the optical disk can be obtained by a common objective lens. It is possible to appropriately form a focused spot focused on the information recording surface.

However, in this case, the divergence angle of the light beam incident on the objective lens OBJ is basically different for the light beams of three wavelengths, and therefore the optical path lengths from the three light sources LD1 to LD3 to the objective lens OBJ do not match. It will be. As a result, the light fluxes of the respective wavelengths focused on the information recording surface of the optical disc are reflected from the information recording surface and then condensed on the places where the optical path lengths from the objective lens OBJ are different (FIG. 2 (a)-(c)). Therefore, in order to obtain the optical information recorded on the information recording surface of the optical disk, if these light beams are received, three light receiving elements are required as shown in FIG. Cost reduction cannot be achieved. On the other hand, if a common light receiving element is used to reduce the size and cost of the optical pickup device, a dichroic prism having wavelength selectivity is used to receive each light beam by the common light receiving element. Therefore, it is necessary to change the optical path length between the objective lens and the light receiving element for each light beam, and the configuration becomes complicated, and the original purpose of compactness cannot be achieved.

In Patent Documents 1 and 2 described above, the coupling lens is either fixed or movable as a whole, and has different effects from the present invention. This will be described. First, light beams having three different wavelengths are assumed to be violet light, red light, and infrared light. When the coupling lens is fixed, if the exit angle can be made different even if the incident angle is the same between the three different wavelengths by providing the coupling lens with a diffractive action, information recording can be made compatible with each optical disc. And / or playback. However, the degree of freedom in designing the objective lens and the coupling lens is remarkably restricted in order to set the emission angles of the three wavelengths to a predetermined value in order to cope with the three different wavelengths. There are harmful effects such as becoming a system.

In particular, the diffractive structure provides a phase difference by forming on the optical surface a fine structure having a level difference corresponding to the wavelength of light to be given a diffraction effect. However, since infrared light (760 nm to 800 nm) is a multiple of the wavelength of blue-violet light (390 nm to 430 nm), the optical element forming the diffractive structure is formed of a material having normal dispersion (νd> 30). If the phase difference is different depending on the step of the fine structure, the infrared light and the blue-violet light that have passed through the fine structure may have the same phase, and the divergence of the light flux is made different based on the difference in wavelength. In both cases, the degree of freedom in design is greatly restricted in order to obtain sufficient diffraction efficiency. For this reason, it becomes difficult to give good aberration to the optical axis shift of the objective lens that occurs when the objective lens follows tracking. Furthermore, when a diffractive structure is formed, there is a problem in that the light use efficiency tends to decrease due to vignetting of light.

In addition, when the entire coupling lens is movable, it is necessary to increase the amount of movement of the coupling lens at the time of wavelength switching in order to give a predetermined divergence (convergence) to the objective lens for light beams of different wavelengths. This is disadvantageous for downsizing of the optical pickup device. In particular, when light beams having three different wavelengths are used, the amount of movement of the coupling lens is larger than when only light beams having two different wavelengths are used. Furthermore, if the amount of movement of the coupling lens increases, there is a problem that the power consumption of the actuator that drives it increases accordingly.

On the other hand, in the present invention, since the coupling lens has a configuration of at least two groups and two or more groups, and one or more groups are movable in the optical axis direction, the three light sources, the objective lens focus, and the light receiving element receive light. Even if the surfaces are conjugated with each other, it is not necessary to provide a diffractive surface on the coupling lens. For this reason, the utilization efficiency of light can be secured high, and the degree of freedom in designing the objective lens and the coupling lens is increased. For example, it is possible to reduce the amount of aberration generated with respect to the deviation of the objective lens from the optical axis of the optical pickup device following the tracking of the objective lens. Moreover, since the amount of movement of the coupling lens is small, it is suitable for downsizing. Compared to the case of using two light beams with different wavelengths in the configuration of the conventional example, the coupling lens needs a larger amount of movement as compared with the case of using light beams with two different wavelengths. On the other hand, as in the present invention, the ability to suppress the amount of movement of the coupling lens is advantageous for downsizing. In the configuration of two or more lenses in two groups, it is preferable from the viewpoint of miniaturization and cost reduction that the lens is configured as two aspherical lenses (two lenses in two groups) and one lens is movable.

The optical pickup device according to claim 2 is the optical pickup device according to claim 1, wherein the first optical information recording medium is a Blu-ray Disc or an HD DVD, and the second optical information recording medium is a DVD, The third optical information recording medium is a CD.

According to a third aspect of the present invention, in the invention of the first or second aspect, the coupling lens is composed of two lenses each having an aspherical surface.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the light beam separation means is a polarization beam splitter, and the NA on the light source side of the coupling lens is 0.12 or less. It is characterized by being.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the at least one group of lenses constituting the coupling lens moves in the optical axis direction, thereby It is characterized by correcting spherical aberration caused by different substrate thicknesses of the information recording medium.

An optical pickup device according to a sixth aspect is characterized in that, in the invention according to any one of the first to fifth aspects, at least two of the three light sources are fixed to a common heat sink. For example, since the optical system can be simplified by using a two-wavelength one-package LD or a three-wavelength one-package LD, the optical pickup device capable of recording and / or reproducing information in a compatible manner can be downsized and reduced. Cost can be reduced. The “heat sink” refers to a member HS or the like that supports the light emitting portion LP that can irradiate two light beams on the stem ST via the submount SM in the two-wavelength one-package LD shown in FIG. An example of such a two-wavelength one-package LD is described in JP-A-2001-215425. When the submount SM is directly attached to the stem ST, the submount SM becomes a heat sink. In addition, when the position portion of the stem ST is raised and the light emitting portion LP is directly attached thereto, the stem ST serves as a heat sink.

According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the at least one group of lenses constituting the coupling lens is driven so as to move in the optical axis direction. It has a drive means.

An optical pickup device according to an eighth aspect of the present invention is the optical pickup device according to the seventh aspect, wherein the driving means includes an electromechanical conversion element, a driving member fixed to one end of the electromechanical conversion element, and the coupling lens. A movable member that is coupled to the at least one group of lenses and that is movably held on the driving member, and changes the speed of the electromechanical conversion element between an extension direction and a contraction direction. And a driving means adapted to move the movable member by repeatedly expanding and contracting.

In the driving means, the electromechanical conversion element is deformed so as to be slightly expanded or contracted by applying a driving voltage such as a sawtooth-shaped pulse to the electromechanical conversion element for a very short time. However, the speed of expansion or contraction can be changed depending on the shape of the pulse. Here, when the electromechanical conversion element is deformed at a high speed in the extending or contracting direction, the movable member does not follow the operation of the driving member due to the inertia of the mass and remains in the same position. On the other hand, when the electromechanical conversion element is deformed in the opposite direction at a slower speed, the movable member moves following the operation of the drive member by the friction force acting therebetween. Therefore, when the electromechanical conversion element repeats expansion and contraction, the movable member can continuously move in one direction. That is, by using the driving means of the present invention having high responsiveness, the at least one group of lenses constituting the coupling lens connected to the movable member can be moved at a high speed and moved by a minute amount. You can also. Further, in the case where the at least one group of lenses constituting the coupling lens is held at a fixed position, if the power supply to the electromechanical conversion element is interrupted, the movable member and the drive member Since it is held by the frictional force acting in between, energy saving can be achieved. In addition, the structure of the driving means is advantageous in that it is simple and can be reduced in size and is low in cost.

According to the present invention, there is provided an optical pickup device capable of recording and / or reproducing information compatible with at least three types of optical information recording media using a common objective lens and a common photodetector. can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 shows a first embodiment in which information can be appropriately recorded / reproduced with respect to a BD (Blu-ray Disc) or HD DVD, DVD and CD, which are optical information recording media having different protective substrate thicknesses. It is a top view which shows the structure of an optical pick-up apparatus roughly. FIG. 5 is a side view of the present embodiment as viewed from the direction of arrow V. In the present embodiment, the condensing optical system includes an objective lens OBJ and a coupling lens COL. The coupling lens COL includes a first group (lenses L1 and L2) and a second group (lens L3). Here, the second group is movable in the optical axis direction. Although the lenses L1 to L3 are not formed with a diffractive structure, a diffractive structure may be formed. In the present embodiment, the second semiconductor laser LD2 as the second light source and the third semiconductor laser LD3 as the third light source are housed in the same package or fixed to the same heat sink. Although two lasers and one package are used, semiconductor lasers may be arranged individually. The three semiconductor lasers LD1 to LD3 and the light receiving portion of the photodetector (light receiving element) PD are optically conjugate with each other via the information recording surfaces of the optical disks OD1 to OD3.

When recording and / or reproducing information with respect to the first optical disk OD1 (for example, BD or HD DVD), the second group of the coupling lens COL is moved to the first position in the optical axis direction, and the semiconductor laser LD1. Is made incident on the objective lens OBJ at the first divergence angle θ1 (see FIG. 12A). Here, in the optical pickup device of FIG. 4, the light beam emitted from the semiconductor laser LD1 (first light source) having a light source wavelength of 390 to 420 nm is shaped by the beam shaping element BS, and further, the first diffraction element D1. After being separated into a main beam for recording / reproducing and a sub beam for detecting a tracking error signal, it is reflected by the dichroic beam splitter DBS, reflected by the polarization beam splitter PBS, and passes through the coupling lens COL. Then, after entering the first divergence angle θ1, the light enters the rising mirror M. The operation of the coupling lens COL will be described later.

In FIG. 5, a part of the light beam incident on the rising mirror M is transmitted through the monitor lens ML, then enters the laser power monitor LPM, and is used for monitoring the laser power. On the other hand, the remainder of the light beam incident on the rising mirror M is reflected there, passes through the quarter-wave plate QWP, and then the objective lens OBJ (in this embodiment, it consists of two elements, but one may be used). Then, the light is focused on the information recording surface R1 of the optical disc OD1 (the thickness of the protective substrate is 0.1 mm or 0.6 mm).

The reflected light beam modulated by the information pits on the information recording surface R1 passes through the objective lens OBJ and the quarter wavelength plate QWP again, is reflected by the rising mirror M, passes through the coupling lens COL, and is further polarized. The light passes through the beam splitter PBS and is condensed on the light receiving surface of the photodetector (light receiving element) PD by the sensor lens SL. A read signal of information recorded on the optical disk OD1 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is moved to the lens holder so that the focusing actuator and tracking actuator of the objective lens actuator mechanism ACT appropriately image the light beam from the first semiconductor laser LD1 on the information recording surface R1 of the optical disk OD1. It is designed to move together with HD.

When recording and / or reproducing information with respect to the second optical disk OD2 (for example, DVD), the second group of the coupling lens COL is moved to the second position in the optical axis direction, and the light beam from the semiconductor laser LD2 Is incident on the objective lens OBJ at the second divergence angle θ2 (see FIG. 12B). Here, in the optical pickup device shown in FIG. 4, the light beam emitted from the semiconductor laser LD2 having a light source wavelength of 630 to 670 nm is emitted from the two lasers 1 package to the outside, and then passes through the second diffraction element D2. Divided into a main beam for recording and reproduction and a sub beam for detecting a tracking error signal, the divergence angle is adjusted by a coupling lens CPL, passes through a half-wave plate HWP, a dichroic beam splitter DBS, and is reflected by a polarizing beam splitter PBS Then, after passing through the coupling lens COL and having the second divergence angle θ2, the light enters the rising mirror M.

In FIG. 5, a part of the light beam incident on the rising mirror M is transmitted through the monitor lens ML, then enters the laser power monitor LPM, and is used for monitoring the laser power. On the other hand, the remainder of the light beam incident on the rising mirror M is reflected there, passes through the quarter-wave plate QWP, and then enters the objective lens OBJ, from which the information recording surface R2 (of the protective substrate) of the optical disk OD2 The light is condensed to a thickness of 0.6 mm.

The reflected light beam modulated by the information pits on the information recording surface R2 passes through the objective lens OBJ and the quarter-wave plate QWP again, is reflected by the rising mirror M, passes through the coupling lens COL, and is further polarized. The light passes through the beam splitter PBS and is condensed on the light receiving surface of the photodetector PD by the sensor lens SL. A read signal of information recorded on the optical disk OD2 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is placed in the lens holder so that the focusing actuator and the tracking actuator of the objective lens actuator mechanism ACT appropriately image the light beam from the second semiconductor laser LD2 on the information recording surface R2 of the optical disk OD2. It is designed to move together with HD.

When recording and / or reproducing information with respect to the third optical disk OD3 (for example, CD), the second group of the coupling lens COL is moved to the third position in the optical axis direction, and the light beam from the semiconductor laser LD3. Is incident on the objective lens OBJ at the third divergence angle θ3 (see FIG. 12C). Here, in the optical pickup device of FIG. 4, a light beam emitted from the semiconductor laser LD3 having a light source wavelength of 760 to 800 nm is emitted from the two lasers 1 package to the outside, and then passes through the second diffraction element D2. Divided into a main beam for recording and reproduction and a sub beam for detecting a tracking error signal, the divergence angle is adjusted by a coupling lens CPL, passes through a half-wave plate HWP, a dichroic beam splitter DBS, and is reflected by a polarizing beam splitter PBS Then, after passing through the coupling lens COL and having the third divergence angle θ3, the light enters the rising mirror M. As for the divergence angles θ1, θ2, and θ3 of the incident light beam on the objective lens OBJ, assuming that the incident light in the diverging state is positive and the incident light in the convergent state is negative, FIG. 12 (a), (b), ( In c), θ1 <0, θ2 <0, and θ3> 0 are satisfied.

In FIG. 5, a part of the light beam incident on the rising mirror M is transmitted through the monitor lens ML, then enters the laser power monitor LPM, and is used for monitoring the laser power. On the other hand, the remainder of the light beam incident on the rising mirror M is reflected there, passes through the quarter-wave plate QWP, and then enters the objective lens OBJ, from which the information recording surface R3 (of the protective substrate) of the optical disk OD3 It is condensed to a thickness of 1.2 mm).

The reflected light beam modulated by the information pits on the information recording surface R3 passes through the objective lens OBJ and the quarter wave plate QWP again, is reflected by the rising mirror M, passes through the coupling lens COL, and is further polarized. The light passes through the beam splitter PBS and is condensed on the light receiving surface of the photodetector PD by the sensor lens SL. A read signal of information recorded on the optical disc OD3 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is moved to the lens holder so that the focusing actuator and the tracking actuator of the objective lens actuator mechanism ACT appropriately image the light beam from the third semiconductor laser LD3 on the information recording surface R3 of the optical disk OD3. It is designed to move together with HD.

According to the present embodiment, the coupling lens COL has a two-group / three-element configuration, and the air interval of each group is variable as will be described later. The divergence angle is changed in accordance with the wavelength of the light beam emitted from each of the semiconductor lasers LD1 to LD3 and the thickness of the protective substrate of the optical disk, thereby forming an appropriate focused spot on the information recording surface of the optical disks OD1 to OD3. it can.

FIG. 6 is a perspective view of an optical system unit CU that integrally accommodates the coupling lens COL and its driving means. In FIG. 6, walls W <b> 1 and W <b> 2 extend upward from both ends of the base B. A guide shaft GS extends so as to connect the vicinity of the upper ends of the walls W1 and W2 (notched). Openings HL through which light beams pass are formed in the walls W1 and W2.

The lenses L1 and L2 are held at the outer periphery by the lens holder HD1 and screwed so as to cover the opening HL of the wall W1. When assembling the lenses L1 and L2, it is desirable to suppress shift and tilt with respect to the reference axis as much as possible by using an autocollimator or the like.

On the other hand, the outer periphery of the lens L3 that is a movable element is held by the lens holder HD2. The lens holder HD2 as a movable member has an engaging portion HDa that engages with the guide shaft GS and a connecting portion HDb that receives a driving force.

The connecting portion HDb is provided with a groove in contact with the drive shaft DS, and a leaf spring SG is attached to the upper surface. A drive shaft DS, which is a drive member, is disposed between the connecting portion HDb and the leaf spring SG, and is appropriately pressed by the urging force of the leaf spring SG. A clearance is provided on the wall W1 side of the drive shaft DS, and the other end passes through the wall W2 and is connected to a piezoelectric actuator PZ that is an electromechanical conversion element. The piezoelectric actuator PZ has a fixing portion Bh, and is fixed to the base B by adhesion or the like outside W2.

On the base B, an encoder (not shown) (position detecting means) that magnetically (or optically) detects the amount of movement of the connecting portion HDb, for example, magnetic information is arranged on the guide shaft GS, and the engaging portion HDa An external drive circuit (not shown) for applying a voltage via the wiring H is disposed to receive a signal from a read head or the like and drive and control the piezoelectric actuator PZ. The piezoelectric actuator PZ, the drive shaft DS, the connecting portion HDb, and the leaf spring SG constitute drive means. The drive circuit may be disposed on the base B and connected by wiring.

The piezoelectric actuator PZ is formed by laminating piezoelectric ceramics formed of PZT (zircon / lead titanate) or the like. Piezoelectric ceramics have a property in which the center of gravity of the positive charge and the center of gravity of the negative charge in the crystal lattice do not coincide with each other, are themselves polarized, and extend when a voltage is applied in the polarization direction. However, since the distortion of the piezoelectric ceramic in this direction is very small and it is difficult to drive the driven member due to the amount of distortion, a plurality of piezoelectric ceramics PE are stacked between the electrodes as shown in FIG. A laminated piezoelectric actuator PZ having a structure in which C is connected in parallel is provided as a practical one. In the present embodiment, this stacked piezoelectric actuator PZ is used as a drive source.

Next, a driving method of the lens L3 by the optical system unit CU will be described. In general, the multilayer piezoelectric actuator PZ has a small amount of displacement when a voltage is applied, but has a large generated force and sharp response. Therefore, as shown in FIG. 8 (a), when a pulse voltage having a substantially sawtooth waveform with a sharp rise and a slow fall is applied, the piezoelectric actuator PZ extends rapidly at the rise of the pulse and more than that at the fall. Shrink slowly. Therefore, when the piezoelectric actuator PZ is extended, the drive shaft DS is pushed out to the back side (wall W1 side) in FIG. 6 by the impact force, but the connecting portion HDb of the lens holder HD2 holding the lens L3 and the leaf spring SG are Due to its inertia, it does not move together with the drive shaft DS, but slips between the drive shaft DS and stays in that position (may move slightly). On the other hand, when the pulse falls, the drive shaft DS returns more slowly than when the pulse rises. Therefore, the connecting portion HDb and the leaf spring SG do not slip with respect to the drive shaft DS, and the drive shaft DS is integrated with the drive shaft DS. Move to the side (wall W2 side). That is, the lens holder HD2 can be continuously moved at a desired speed by applying a pulse whose frequency is set to several hundred to several tens of thousands of hertz. As is clear from the above, as shown in FIG. 8B, the lens holder HD2 can be moved in the opposite direction by applying a pulse in which the voltage rises slowly and sharply falls. In particular, if the guide shaft GS is straight, the lens holder HD2 moves with high precision in the optical axis direction, and aberration deterioration can be effectively suppressed as compared with the case where the optical axis shift occurs due to driving.

FIG. 9 shows a second embodiment in which information can be recorded / reproduced appropriately for BD (Blu-ray Disc) or HD DVD, DVD, and CD, which are optical information recording media having different protective substrate thicknesses. It is a top view which shows the structure of an optical pick-up apparatus roughly. Also in the present embodiment, an objective lens OBJ and a coupling lens COL are included as a condensing optical system. The coupling lens COL includes a first group (lens L1) and a second group (lens L2). Here, the second group is movable in the optical axis direction. 6 to 8 can be used as the second group of driving means. The lenses L1 and L2 have aspheric surfaces and no diffractive structure is formed, but a diffractive structure may be formed. The three semiconductor lasers LD1 to LD3 and the light receiving portion of the photodetector (light receiving element) PD are optically conjugate with each other via the information recording surfaces of the optical disks OD1 to OD3.

When recording and / or reproducing information with respect to the first optical disk OD1 (for example, BD or HD DVD), the second group of the coupling lens COL is moved to the first position in the optical axis direction, and the semiconductor laser LD1. Is made incident on the objective lens OBJ at the first divergence angle θ1. Here, in the optical pickup device of FIG. 9, the P-polarized light beam emitted from the semiconductor laser LD1 (first light source) having a light source wavelength of 390 to 420 nm is emitted from the first dichroic prism DBS1, the second dichroic prism DBS2, and the like. The light passes through the polarization beam splitter PBS, passes through the coupling lens COL, has the first divergence angle θ1, and further passes through the quarter-wave plate QWP, and then enters the objective lens OBJ. The light is focused on the information recording surface R1 (the thickness of the protective substrate is 0.1 mm or 0.6 mm).

The reflected light beam modulated by the information pits on the information recording surface R1 passes through the objective lens OBJ and the quarter wavelength plate QWP again to become S-polarized light, passes through the coupling lens COL, and is reflected by the polarizing beam splitter PBS. Thereafter, the light is condensed on the light receiving surface of the photodetector (light receiving element) PD by the sensor lens SL. A read signal of information recorded on the optical disk OD1 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is configured so that the focusing actuator and the tracking actuator of the objective lens actuator mechanism (not shown) appropriately form the light beam from the first semiconductor laser LD1 on the information recording surface R1 of the optical disc OD1. Is moved together with the lens holder HD.

When recording and / or reproducing information with respect to the second optical disk OD2 (for example, DVD), the second group of the coupling lens COL is moved to the second position in the optical axis direction, and the light beam from the semiconductor laser LD2 Is incident on the objective lens OBJ at the second divergence angle θ2. Here, in the optical pickup device of FIG. 9, the P-polarized light beam emitted from the semiconductor laser LD2 (second light source) having a light source wavelength of 630 to 670 nm is reflected by the first dichroic prism DBS1, and is then second dichroic. The light passes through the prism DBS2 and the polarization beam splitter PBS, passes through the coupling lens COL, is set to the second divergence angle θ2, and further passes through the quarter-wave plate QWP, and then enters the objective lens OBJ. The light is condensed on the information recording surface R2 (protective substrate thickness 0.6 mm) of the optical disc OD2.

The reflected light beam modulated by the information pits on the information recording surface R2 passes through the objective lens OBJ and the quarter wavelength plate QWP again to become S-polarized light, passes through the coupling lens COL, and is reflected by the polarizing beam splitter PBS. Thereafter, the light is condensed on the light receiving surface of the photodetector (light receiving element) PD by the sensor lens SL. A read signal of information recorded on the optical disk OD2 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is configured so that the focusing actuator and the tracking actuator of the objective lens actuator mechanism (not shown) appropriately form the light beam from the second semiconductor laser LD2 on the information recording surface R2 of the optical disk OD2. Is moved together with the lens holder HD.

When recording and / or reproducing information with respect to the third optical disk OD3 (for example, CD), the second group of the coupling lens COL is moved to the third position in the optical axis direction, and the light beam from the semiconductor laser LD3. Is incident on the objective lens OBJ at the third divergence angle θ3. Here, in the optical pickup device of FIG. 9, the P-polarized light beam emitted from the semiconductor laser LD3 (third light source) having a light source wavelength of 760 to 800 nm is reflected by the second dichroic prism DBS2, and is polarized by the polarization beam splitter PBS. , Passes through the coupling lens COL, is set to the third divergence angle θ3, and further passes through the quarter-wave plate QWP, then enters the objective lens OBJ, and from there, the information recording surface R3 of the optical disc OD3 The light is focused on (the thickness of the protective substrate is 1.2 mm).

The reflected light beam modulated by the information pits on the information recording surface R3 passes through the objective lens OBJ and the quarter wavelength plate QWP again to become S-polarized light, passes through the coupling lens COL, and is reflected by the polarizing beam splitter PBS. Thereafter, the light is condensed on the light receiving surface of the photodetector (light receiving element) PD by the sensor lens SL. A read signal of information recorded on the optical disc OD3 is obtained using the output signal of the photodetector PD.

In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective lens OBJ is configured so that the focusing actuator and the tracking actuator of the objective lens actuator mechanism (not shown) appropriately form the light beam from the third semiconductor laser LD3 on the information recording surface R3 of the optical disc OD3. Is moved together with the lens holder HD.

In the present embodiment, light beams of three different wavelengths emitted from the light source are transmitted through the polarization beam splitter PBS provided on the light source side of the coupling lens COL, and light beams of three different wavelengths reflected from the optical disk are transmitted. reflect. For these three wavelengths λ1, λ2, and λ3, it is preferable to have coat characteristics of Tp (light transmittance of P-polarized light) ≧ 80% and Rs (light transmittance of S-polarized light) ≧ 80%. In order to achieve this, if the light source side NA of the coupling lens is 0.12 or less, the number of layers of the polarizing beam splitter PBS may be 40 or less, which is advantageous for reducing the cost of the polarizing beam splitter PBS. Furthermore, it is possible to suppress the occurrence of spherical aberration accompanying the change in the thickness of the optical disk by moving the coupling lens COL in the optical axis direction.

Note that there are two types of polarization beam splitter PBS: a type in which the formed polarization beam splitter surface is in contact with air and a type in which the polarization beam splitter surface is not in contact with air. Of these, the polarization beam splitter PBS of the type in which the formed polarization beam splitter surface is sandwiched between glass and does not come into contact with air, as in the above-described embodiment, has a light beam incident angle dependency on the polarization beam splitter characteristics. The design and production of a reduced coat becomes easy. Therefore, in the optical pickup device in which the optical element is arranged so that the light beam emitted from the polarization beam splitter surface enters the coupling lens COL without changing the divergence of the light beam, the light source side NA of the coupling lens COL is set to 0. When a relatively large value of .05 or more is used, it is desirable to use a polarization beam splitter of a type in which the formed polarization beam splitter surface does not contact air. In particular, when the light source side NA of the coupling lens COL is 0.07 or more, it is preferable from the viewpoint of the cost of the optical pickup device that the polarizing beam splitter surface is a type that does not contact air.

FIG. 10 shows a third embodiment in which information can be recorded / reproduced appropriately for BD (Blu-ray Disc) or HD DVD, DVD and CD, which are optical information recording media having different protective substrate thicknesses. It is a top view which shows the structure of this optical pick-up apparatus roughly. This embodiment is different from the embodiment shown in FIG. 9 in that a coupling lens CL1 is inserted between the first semiconductor laser LD1 and the first dichroic prism DBS1, and the second semiconductor laser LD2 and the first dichroic prism are inserted. The only difference is that the coupling lens CL2 is inserted between the DBS2 and the coupling lens CL3 is inserted between the third semiconductor laser LD3 and the second dichroic prism DBS2. Also in the present embodiment, the three semiconductor lasers LD1 to LD3 and the light receiving portion of the photodetector (light receiving element) PD have an optically conjugate relationship with each other via the information recording surfaces of the optical disks OD1 to OD3. It has become.

According to the present embodiment, since the light beams emitted from the respective semiconductor lasers LD1 to LD3 are converted into parallel light beams by the respective coupling lenses CL1 to CL3, they are all incident on the coupling lens COL in a state of parallel light beams. To do. However, the coupling lens COL emits a light beam at a predetermined divergence angle by moving the second group thereof to the first to third positions in the optical axis direction according to the optical disk to be used, and to the objective lens OBJ. Since it is made incident, spherical aberration can be suppressed as described above.

FIG. 11 shows a fourth embodiment in which information can be recorded / reproduced appropriately for BD (Blu-ray Disc) or HD DVD, DVD and CD, which are optical information recording media having different protective substrate thicknesses. It is a top view which shows the structure of an optical pick-up apparatus roughly. This embodiment is different from the embodiment shown in FIG. 9 in that a coupling lens CL3 is inserted between the first semiconductor laser LD1 and the first dichroic prism DBS1, and the second semiconductor laser LD2 and the first dichroic prism are inserted. Only the coupling lens CL2 is inserted between the DBS1 and the DBS1. Also in the present embodiment, the three semiconductor lasers LD1 to LD3 and the light receiving portion of the photodetector (light receiving element) PD have an optically conjugate relationship with each other via the information recording surfaces of the optical disks OD1 to OD3. It has become.

According to the present embodiment, since the light beams emitted from the semiconductor lasers LD1 and LD2 are converted into parallel light beams by the coupling lenses CL1 and CL2, both are incident on the coupling lens COL in the state of parallel light beams. To do. However, since the light beam emitted from the semiconductor laser LD3 is incident on the coupling lens COL in the state of a finite divergent light beam, it can correspond to a protective substrate thickness of CD of 1.2 mm. Further, the coupling lens COL emits a light beam at a predetermined divergence angle by moving the second group to the first to third positions in the optical axis direction according to the optical disk to be used, and to the objective lens OBJ. Since it is made incident, spherical aberration can be suppressed as described above.

Next, examples suitable for the above-described embodiment will be described. Table 1 shows lens data of this example. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5E-3).

The optical surface of the objective optical system is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 2.

Further, the optical path length given to the light flux of each wavelength by the diffractive structure is defined by a mathematical formula in which the coefficient shown in Table 1 is substituted into the optical path difference function of Formula 3.

The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. The two-laser one package may be a combination of the first semiconductor laser LD1 and the second semiconductor laser LD2. Further, a plurality of driving means may be provided instead of a single one.

It is the schematic of the optical pick-up apparatus as a comparative example which arrange | positions the three light sources from which a wavelength differs in the position where the light beam which injects into an objective lens respectively becomes a predetermined divergence angle. It is a figure which shows the positional relationship of each light source and each light receiving element in the case of recording and / or reproducing | regenerating information with respect to each optical disk. It is a perspective view which shows an example of 2 laser 1 package. It is a top view which shows roughly the structure of the optical pick-up apparatus concerning 1st Embodiment. It is the figure which looked at the structure of FIG. 1 in the arrow II direction. It is a perspective view of the optical system unit CU which integrally accommodated the coupling lens COL and its drive part. FIG. 3 is a perspective view showing a multilayer piezoelectric actuator PZ having a structure in which a plurality of piezoelectric ceramics PE are stacked and electrodes C are connected in parallel therebetween. It is a figure which shows the waveform of the voltage pulse applied to the piezoelectric actuator PZ. It is a figure which shows schematically the structure of the optical pick-up apparatus concerning 2nd Embodiment. It is a figure which shows schematically the structure of the optical pick-up apparatus concerning 3rd Embodiment. It is a figure which shows schematically the structure of the optical pick-up apparatus concerning 4th Embodiment. It is a figure which shows the relationship between the position of a coupling lens, and the divergence angle of the light beam radiate | emitted from a coupling lens, (a) has a coupling lens in a 1st position, and the divergence angle in that case is (theta) 1 In (b), the coupling lens is in the second position, and the divergence angle is θ2, and in (c), the coupling lens is in the third position, and the divergence angle is θ3. is there.

Explanation of symbols

θ1 divergence angle θ2 divergence angle θ3 divergence angle λ1 first wavelength λ2 second wavelength λ3 third wavelength ρ1 first recording density ρ2 second recording density ρ3 third recording density ACT objective lens actuator mechanism B base BS Beam shaping element Bh Fixed portion C Electrode CL1 First coupling lens CL2 Second coupling lens CL3 Third coupling lens COL Coupling lens CPL Coupling lens CU Optical system unit D1 Diffraction element D2 Diffraction element DBS Dichroic beam Splitter DBS1 Dichroic prism DBS2 Dichroic prism DBS2, Dichroic prism DS Drive shaft GS Guide shaft H Wiring HD Lens holder HD1 Lens holder HD2 Lens holder HDa Engaging portion HDb Connecting portion HL Opening HS Member HWP Wave plate L1 Lens L2 lens L3 lens LD package LD1 first semiconductor laser LD2 second semiconductor laser LD3 third semiconductor laser LP light emitting part LPM laser power monitor M mirror ML monitor lens OBJ objective lens OD1 first optical disk OD2 second optical disk OD3 second Optical disk PBS 3 Polarizing beam splitter PD Photodetector PE Piezoelectric ceramics PZ Piezoelectric actuator PZ Laminated piezoelectric actuator QWP λ / 4 wave plate R1 First information recording surface R2 Second information recording surface R3 Third information recording surface SL Sensor lens SM Submount ST Stem W1 Wall W2 Wall

Claims

A first light source that emits a light beam with a wavelength λ1 of 390 to 420 nm, a second light source that emits a light beam with a wavelength λ2 of 630 to 670 nm, and a third light source that emits a light beam with a wavelength λ3 of 760 to 800 nm An objective lens for condensing the light beam from the light source on the information recording surface of the optical information recording medium; and in the common optical path of the light beams emitted from the first, second, and third light sources, and the light source The coupling lens disposed in the optical path with the objective lens, the light beam reflected from the information recording surface of the optical information recording medium, the light beam separating means for separating the light beam from the light source, and the light beam separating means for separation. A light receiving element that receives the light beam reflected from the information recording surface of the optical information recording medium,
The coupling lens is composed of two or more lenses in two groups, and at least one group of the constituting lenses is arranged to be movable in the optical axis direction.
A light receiving unit for receiving the light beam emitted from the first light source, the light beam emitted from the second light source, and the light beam emitted from the third light source is provided in one light receiving element. Packaged,
The light beam emitted from the first light source, the light beam emitted from the second light source, and the light beam emitted from the third light source reflected from the information recording surface of the optical information recording medium are common. Is received by the light receiving portion of the light receiving element through the optical element,
The luminous flux emitted from the first light source is incident on the objective lens after being given a first divergence angle (θ1) by the coupling lens in which the at least one group has moved to the first position. The information is recorded and / or reproduced by being condensed on the information recording surface of the first information recording medium having the recording density ρ1,
The luminous flux emitted from the second light source is given a second divergence angle (θ2) by the coupling lens in which the at least one group has moved to the second position, and then recorded by the objective lens. Information is recorded and / or reproduced by being condensed on the information recording surface of the second information recording medium having a density ρ2 (ρ1> ρ2).
The light beam emitted from the third light source is given a third divergence angle (θ3) by the coupling lens in which the at least one group has moved to the third position, and then recorded by the objective lens. Information is recorded and / or reproduced by being condensed on the information recording surface of the third information recording medium having a density ρ3 (ρ2> ρ3).
The optical pickup device, wherein the three light sources and the light receiving portion of the light receiving element are optically conjugate with each other via an information recording surface of each optical information recording medium.
2. The first optical information recording medium is a Blu-ray Disc or HD DVD, the second optical information recording medium is a DVD, and the third optical information recording medium is a CD. The optical pickup device described.
The optical pickup device according to claim 1, wherein the coupling lens includes two lenses each having an aspheric surface.
4. The optical pickup device according to claim 1, wherein the light beam separating means is a polarization beam splitter, and the NA on the light source side of the coupling lens is 0.12 or less.
The spherical aberration caused by different substrate thicknesses of the optical information recording medium is corrected by moving the at least one group of lenses constituting the coupling lens in the optical axis direction. Item 5. The optical pickup device according to any one of Items 1 to 4.
The optical pickup device according to claim 1, wherein at least two of the three light sources are fixed to a common heat sink.
The optical pickup device according to claim 1, further comprising: a driving unit that drives the at least one group of lenses constituting the coupling lens so as to move in the optical axis direction.
The drive means is connected to the electromechanical conversion element, a drive member fixed to one end of the electromechanical conversion element, and the at least one group of lenses constituting the coupling lens, and is moved onto the drive member And a movable member that is held so as to move the movable member by repeatedly expanding and contracting the electromechanical conversion element at different speeds in the extending direction and the contracting direction. The optical pickup device according to claim 7, further comprising: