WO2005048249A1 - Optical pickup and optical disc drive - Google Patents

Abstract

An optical pickup for an optical recording medium (1) having a plurality of recording faces (1a, 1b), wherein a light source, having a plurality of laser light emitting sections (a, b) that are provided for respective recording faces (1a, 1b) and adjusted and set in the mutual positions in the direction of optical axis such that spherical aberration does not occur due to the optical characteristics of laser light being applied to the corresponding recording face (1a, 1b) through a common objective lens (8), is provided. Since recording or reproducing operation can be carried out using the light emitting section (a, b) corresponding to the recording face (1a, 1b), a good recording or reproducing operation can be realized using a small and low-cost optical system as compared with that employing a wave aberration correction element, e.g. a liquid crystal element.

Description

 Specification

 Optical pickup device and optical disk device

 Technical field

 The present invention relates to an optical pickup device and an optical disk device.

 Background art

 [0002] Conventionally, there has been a proposal in which a liquid crystal element is used to correct the influence of spherical aberration on an optical disc having a plurality of recording layers (recording surfaces) (for example, see Patent Document 1).

 Patent Document 1: JP-A-10-20263

 Disclosure of the invention

 Problems to be solved by the invention

[0003] In recent years, it has been required to increase the recording density of optical discs as the amount of information increases.

 Therefore, the recording density of the optical disc has been increased by increasing the linear recording density in the information recording layer of the optical disc and by narrowing the track pitch. In order to cope with the higher recording density of the optical disk, it is necessary to reduce the beam diameter of the light beam focused on the information recording layer of the optical disk. Methods for reducing the beam diameter of the light beam include increasing the numerical aperture NA (Numerical Aperture) of the light beam emitted from an objective lens as a condensing optical system of an optical pickup device for recording and reproducing an optical disk, It is possible to shorten the wavelength of the light beam. For example, shortening the wavelength of a light beam is considered to be feasible by changing the light source to a red semiconductor laser, a blue-violet semiconductor laser that has begun to be fully commercialized.

[0004] In general, in an optical disc, the information recording layer is covered with a cover glass in order to protect the information recording layer from dust and scratches. Therefore, the light beam transmitted through the objective lens of the optical pickup device passes through the cover glass, and is condensed and focused on the information recording layer thereunder. When the light beam passes through the cover glass in this way, spherical aberration SA (Spherical Aberration) occurs. The spherical aberration SA is represented by the following equation (1).

SAocd-NA ⁴ That is, the spherical aberration SA is proportional to the fourth power of the cover glass thickness d and the numerical aperture NA of the objective lens. Usually, the objective lens is designed to cancel the spherical aberration, so that the spherical aberration of the light beam passing through the objective lens and the cover glass is sufficiently small.

 [0005] However, if the thickness of the cover glass deviates from a predetermined value, a spherical aberration occurs in the light beam focused on the information recording layer, and the beam diameter increases. Information cannot be read and written correctly. Also, according to the above equation (1), the spherical aberration error ASA caused by the cover glass thickness error Ad is proportional to the cover glass thickness error △ (!. That is, the cover glass thickness error Ad can be increased. The greater the error, the greater the spherical aberration error ASA, which makes it impossible to read and write information correctly.

 [0006] In a conventional optical disc, for example, like a DVD (Digital Versatile Disc), the numerical aperture NA of an objective lens in an optical pickup device used is as small as about 0.6. Therefore, the spherical aberration error ASA caused by the cover glass thickness error Ad was small, and the light beam could be focused sufficiently small for each information recording layer. On the other hand, as a multi-layer optical disc formed by laminating information recording layers, for example, a DVD with two information recording layers has already been commercialized so that the density of recorded information can be increased in the thickness direction of the optical disc. Has been developed. In an optical pickup device for recording and reproducing such a multilayer optical disk, it is necessary to focus a light beam sufficiently small for each information recording layer of the optical disk. However, in the above-described multilayer optical disc, the thickness from the surface of the optical disc (cover glass surface) to each information recording layer differs for each of the laminated information recording layers. Thus, the spherical aberration generated when the light beam passes through the cover glass of the optical disc differs for each information recording layer. In this case, for example, the difference (error ASA) of the spherical aberration occurring in the information recording layer in contact with the P is in proportion to the interlayer distance t (corresponding to the thickness d) of the information recording layer in contact with the above equation (1). .

[0007] Even if the cover glass thickness error Ad is equal, the larger the numerical aperture NA, the greater the spherical aberration SA occurs. For example, when NA = 0.85 compared to NA = 0.6, approximately four times the spherical aberration SA occurs. Therefore, from the above equation (1), a high numerical aperture such as NA = 0.85 can be obtained. The more it becomes, the larger the spherical aberration caused by the cover glass thickness error Ad becomes.

 Therefore, in multilayer recording / reproducing, it is necessary to correct the influence of spherical aberration. However, as described in Patent Document 1, for example, a measure using a liquid crystal element requires a liquid crystal element body and a drive circuit system for driving the liquid crystal element. As a result, the cost of the optical disk device is greatly increased. In addition, the liquid crystal element itself must be arranged in the optical path of the optical system, which is a major obstacle to downsizing the optical pickup device.

 [0008] An object of the present invention is to reduce the cost and the size of a device using a wavefront aberration correction element such as a liquid crystal element so that the recording or reproducing operation on an optical recording medium having a plurality of recording surfaces is affected by the wavefront aberration. Is to be able to do without.

 Means for solving the problem

[0009] In order to achieve the above object, the present invention relates to an optical pickup device for irradiating an optical recording medium having a plurality of recording surfaces laminated thereon, wherein a laser beam is applied to the optical recording medium. An objective lens for converging and irradiating, and a light source provided for each recording surface and having a plurality of laser light emitting units for emitting laser light for irradiating a corresponding recording surface through the objective lens. Further, the present invention also provides an optical disk device provided with the above optical pickup device.

 The invention's effect

 According to the present invention, it is possible to realize a better recording or reproducing operation at a lower cost and a smaller size than an optical system using a wavefront aberration correcting element such as a liquid crystal element.

 Brief Description of Drawings

 FIG. 1 is an optical system configuration diagram schematically showing a configuration example of an optical pickup device according to an embodiment of the present invention provided in an optical disk device.

 FIG. 2 is an explanatory diagram schematically showing an optical system of a semiconductor laser chip separated.

 FIG. 3 is a perspective view showing a configuration example of a light source unit.

 FIG. 4 is a diagram showing a configuration example of an optical disc device according to an embodiment of the present invention.

Explanation of reference numerals [0012] 1 DVD disk (optical recording medium)

 la, lb recording surface

 2 Optical pickup device

 3 LD package (light source)

 4 Diffraction grating

 5 Deflection beam splitter

 6 Collimator lens

 7 1/4 wave plate

 8 Objective lens

 9 Cylindrical lens

 10 Light receiving element

 11a, l ib Semiconductor laser chip (light emitting unit)

 12a, 12b p electrode

 13a, 13b n electrode

 20 Optical disk drive

 21 Spin Dole Motor

 22 Servo circuit

 23 Optical Disk Controller

 24 Access control circuit

 25 Signal processing circuit

 26 Interface

 a, b Light emitting point

 BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an optical system configuration diagram schematically showing a configuration example of an optical pickup device provided in an optical disk device according to an embodiment of the present invention. In the embodiment shown in FIG. 1, a DVD disc is used as an optical recording medium.

The optical pickup device 2 shown in FIG. 1 irradiates the optical recording medium 1 with a wavelength of about 660 nm. An LD package 3 as a light source that emits a laser beam, a diffraction grating 4 for separating the laser beam emitted from the LD package 3 into three beams, for example, a main beam and two sub beams, and incident light. Polarizing beam splitter 5 for separating return light, collimator lens ₆ for collimating divergent laser light, 1Z4 wave plate 7 for converting linearly polarized light to circularly polarized light, and focusing and irradiating laser light on recording surface Objective lens 8, a cylindrical lens 9 for condensing the return light separated by the polarizing beam splitter 5, and receiving the condensed return light to detect RF signal information, servo signals, etc. And a light-receiving element 10 having an appropriately divided structure for performing the operation.

 In such a basic configuration, the laser light emitted from the LD package 3 passes through the polarizing beam splitter 5 and the collimator lens 6 while being separated into three beams by the diffraction grating 4, and becomes a quarter-wavelength parallel light flux. The light enters the plate 7, is converted from linearly polarized light into circularly polarized light, and is condensed and irradiated on the recording surface of the optical recording medium 1 by the objective lens 8. In this case, the three spots based on the three beams are separately irradiated at predetermined intervals.

 The return light reflected from the optical recording medium 1 passes through the objective lens 8 and the quarter-wave plate 7 again, and is converted from circularly polarized light into linearly polarized light having a polarization direction different from that of the incident light by 90 °. Then, the light enters the polarization beam splitter 5. As a result, the return light is separated from the incident light and condensed on the light receiving element 10 by the cylindrical lens 9. RF signal information, servo signals, and the like are detected based on the light receiving signal of the light receiving element 10.

 In such a basic configuration, the embodiment shown in FIG. 1 is a DVD having a plurality of recording surfaces, for example, a DVD having two recording surfaces, a first recording surface la and a second recording surface lb. Disc 1 is applicable. Therefore, in order to correspond to such a plurality of recording surfaces, the optical pickup device 2 has a semiconductor laser chip 1 la, which serves as two light emitting units dedicated to each of the recording surfaces la and lb with respect to the LD package 3. Consists of 1 lb.

 That is, the semiconductor laser chip 11a is provided for the recording surface la of the first layer, and the semiconductor laser chip l ib is provided for the recording surface lb of the fourth layer. Each of these semiconductor laser chips 11a and 11b emits laser light having a wavelength of about 660 nm from the light emitting point corresponding to the DVD disk 1.

Further, the semiconductor laser chips 11a and 11b are located between the light emitting point positions in the optical axis direction. The positional relationship between the recording surfaces la and lb is adjusted and set so that the distance becomes a predetermined distance according to the distance between the recording surfaces la and lb.

That is, when the laser light emitted from the semiconductor laser chip 11a is applied to the first-layer recording surface la via an optical system such as the objective lens 8 or the like, the laser light is emitted from the semiconductor laser chip 11a. Is positioned at the position on the optical axis where the optical characteristics (recording / reproducing function) are optimal. Similarly, when the laser light emitted from the semiconductor laser chip l ib is applied to the second layer recording surface lb via an optical system such as the objective lens 8, the laser beam emitted from the semiconductor laser chip l ib is The laser beam is positioned on the optical axis at which the optical characteristics (recording / reproducing function) of the laser beam are optimal (ie, a state in which spherical aberration is extremely small). As a result, these semiconductor laser chips 11a and 11b are arranged so as to have a predetermined distance between light emitting point positions in the optical axis direction.

 Next, the specific setting of the distance will be described with reference to FIG. 2, which schematically shows the optical system of the semiconductor laser chips 11a and 11b separately. Now, the focal length of the collimator lens 6 is fcl, the focal length of the objective lens 8 is fol, the distance between the first and second recording surfaces la and lb is d, and the distance between the first and second recording surfaces la and lb. Assuming that the refractive index is n, the distance L between the light emitting points a and b in the optical axis direction of the two semiconductor laser chips 11a and lib is

L = (fol / fcl) ² X nd

 The positions in the optical axis direction are adjusted and set so as to satisfy the following relationship.

According to the configuration of the optical pickup device 2 of the present embodiment, the mutual optical axes are adjusted so that the optical characteristics of the laser light radiated to the corresponding recording surfaces la and lb via the common objective lens 8 are optimized. An LD package 3 having two semiconductor laser chips l la and l ib whose position in the direction is adjusted is provided. Therefore, the optical pickup device 2 uses a wavefront aberration correction element such as a liquid crystal element that performs a recording or reproducing operation using the semiconductor laser chips 1 la and 1 lb corresponding to the respective recording surfaces la and lb. An excellent recording or reproducing operation can be realized with a lower cost and a smaller size than the optical system.

That is, each of the semiconductor laser chips l la and l ib is adjusted and set so that the optical characteristics with respect to the first and second recording surfaces la and lb of the DVD disk 1 are optimal. At the time of recording or reproducing operation of the first layer recording surface la, the semiconductor laser chip 11a is used and the second layer The use of the semiconductor laser chip l ib during the recording or reproducing operation of the recording surface lb of will not be affected by spherical aberration during the recording or reproducing operation of any of the recording surfaces la and lb.

Incidentally, the mutual positional relationship between the semiconductor laser chips l la and l ib is designed and managed so that the mutual positional relationship in the optical axis direction becomes a predetermined value by simultaneous fabrication in the fabrication stage of these chips. It is desirable to keep. Here, a configuration example of the light source unit will be described with reference to FIG. As shown in FIG. 3, the semiconductor laser chips 11a and 11b are formed adjacently and simultaneously on the same substrate. Then, the positions are set by cutting the semiconductor laser chips 11a and 11b so that the distance in the optical axis direction between the light emitting points a of the laser beams 11a and lib satisfies the above relational expression relating to L. In FIG. 3, 12a and 12b are p electrodes of each chip, and 13a and 13b are n electrodes. As described above, if the light emitting section is configured as a semiconductor laser chip and the positional relationship between the chips in the optical axis direction is designed, managed, and adjusted at the manufacturing stage, it is possible to manufacture the semiconductor laser chip with high accuracy and at a later time. It is also possible to eliminate the necessity of adjusting the positional relationship by using.

 Although the present embodiment has been described with reference to an example in which the present invention is applied to a DVD disk 1 having two recording surfaces la and lb, an optical recording medium having three or more recording surfaces The same can be applied to The optical recording medium is not limited to a DVD disk, but may be a CD disk using a laser beam having a wavelength of about 780 nm, or an optical pickup device capable of recording and reproducing both CDZDVD disks. Les ,. Furthermore, in the present embodiment, the force applied to an example of an optical system configuration called a Balta type using the light source 3 and the light receiving element 10 separately is a light receiving / emitting element recently used in an optical pickup configuration. It is a matter of course that a hologram unit that installs a hologram or a polarization hologram in one package and separates and combines light beams by using a hologram unit or an optical system configuration that uses a polarization hologram unit may be used. .

Next, an optical disk device provided with the optical pickup device 2 will be described with reference to FIG. FIG. 4 is a diagram illustrating a configuration example of an optical disc device according to an embodiment of the present invention. The optical disk device 20 includes an optical pickup device 2, a spin-driving motor 21, a servo circuit 22, an optical disk controller 23, an access control circuit 24, a signal processing circuit 25, and an Interface 26.

 The spindle motor 21 drives the optical recording medium 1 to rotate at a predetermined rotation speed under the control of the optical disk controller 23. The servo circuit 22 performs focus servo and tracking servo of the optical pickup device based on a tracking error signal, a focus error signal, and the like under the control of the optical disk controller 23.

 The access control circuit 24 operates the optical pickup device 2 at high speed in the radial direction of the optical recording medium 1 under the control of the optical disk controller 23, and moves the optical pickup device 2 on the signal recording surface of the optical recording medium 1. At a predetermined recording track. The access control circuit 24 also controls the emission power of the laser light emitted from the optical pickup device 2 under the control of the optical disk controller 23.

 The signal processing circuit 25 generates a reproduction signal based on the detection signal from the optical pickup device 2. The generated reproduction signal is output to an external computer or the like via the interface 26. Thus, an external computer or the like can receive a signal recorded on the optical recording medium 1 as a reproduction signal. Further, the signal processing circuit 25 generates a control signal such as a tracking error signal or a focus error signal based on the detection signal from the optical pickup device 2 and outputs the control signal to the optical disk controller 25.

 As described above, in the optical disk device 20 shown in FIG. 4, by providing the optical pickup device 2 described above, it is possible to provide an optical disk device that realizes a good recording or reproducing operation at low cost and small size. Can be.

 As described above, according to the present invention, an optical pickup device for an optical recording medium having a plurality of recording surfaces or an optical disk device including the above optical pickup device is provided for each recording surface. Since a light source having a plurality of laser light emitting units for emitting laser light to irradiate the corresponding recording surface through a common objective lens is provided, if the recording or reproducing operation is performed using the light emitting unit corresponding to each recording surface, This makes it possible to realize a good recording or reproducing operation at a lower cost and a smaller size than an optical system using a wavefront aberration correcting element such as a liquid crystal element. In particular, the light emitting section is configured as a semiconductor laser chip, and the positional relationship between the chips in the optical axis direction is designed, managed and adjusted at the manufacturing stage, so that the device can be manufactured accurately and the positional relationship can be adjusted later Can be eliminated.

Claims

The scope of the claims  [1] Light t applied to an optical recording medium having a plurality of recording surfaces stacked  And  An objective lens for converging and irradiating a laser beam on the optical recording medium;  A light source that is provided for each recording surface and has a plurality of laser emitting units that emit laser light that irradiates the corresponding recording surface via the objective lens;  An optical pickup device comprising:  [2] The light source according to [1], wherein the light sources are arranged in a single package such that light emitting points of a plurality of semiconductor laser chips each serving as the light emitting unit are brought close to each other in a direction perpendicular to an optical axis. Optical pickup device.  [3] The focal length of the collimator lens for collimating the laser light emitted from the light source is fcl, the focal length of the objective lens is fol, the distance between the recording surfaces is d, and the refractive index between the recording surfaces is n. Then, the distance L between the light emitting point positions of the two semiconductor laser chips in the optical axis direction with respect to the recording surface in contact with P is L = (fol / fcl) ² X nd  3. The optical pickup device according to claim 2, wherein the positions in the optical axis direction are adjusted and set so as to satisfy the following relationship.  [4] The position of the semiconductor laser chip in the optical axis direction is adjusted and set by simultaneous production of two semiconductor laser chips on an adjacent recording surface in a production step of the semiconductor laser chip. 2. The optical pickup device according to 2.  5. The method according to claim 5, wherein, in the step of manufacturing the semiconductor laser chip, the positions in the optical axis direction are adjusted and set by simultaneously manufacturing two semiconductor laser chips on adjacent recording surfaces. The optical pickup device according to 3.  [6] An optical disk device comprising the optical pickup device according to claim 1. [7] An optical disc device comprising the optical pickup device according to claim 2. [8] An optical disc device comprising the optical pickup device according to claim 3. [9] An optical disc device comprising the optical pickup device according to claim 4. [10] An optical disc device comprising the optical pickup device according to claim 5.