Optical integrated device, optical pickup and optical disk apparatus

1. Field of the Invention

The present invention relates to an optical integrated device, an optical pickup, and an optical disk apparatus, and is applicable to an optical disk apparatus for playing back a compact disk and a DVD (Digital Video Disk). The present invention resides in dividing feedback light with a diffraction grating and detecting the divided feedback light with a light-detecting element. Laser beam sources having different wavelengths are spaced a predetermined distance from each other in order to make up for the difference between diffraction angles of the diffraction grating thereby enabling access to a plurality of types of optical disks with a simple arrangement.

2. Brief Description of the Related Art

Conventional compact disk players as optical disk apparatus have an optical pickup which applies a laser beam to the information-recorded surface of a compact disk and processes detected feedback light of the applied laser beam for thereby reproducing various types of data recorded on the compact disk.

Optical pickups for such compact disk players are classified into a group in which a light-emitting element and a light-detecting element are disposed independently of each other, and another group in which a light-emitting element and a light-detecting element are integrally combined with each other. The optical pickups of the latter group are smaller in size and more reliable than the optical pickups of the former group.

Optical disk apparatus for playing back DVDs may be reduced in size and simplified in structure if their optical pickup is constructed using an optical integrated device. It is considered highly convenient if such optical disk apparatus for playing back DVDs are capable of playing back compact disks.

In such an application, if a light-emitting element and a light-detecting element for DVDs and a light-emitting element and a light-detecting element for compact disks are integrally combined into an optical integrated device, then an optical disk apparatus can be constructed which is capable of playing back both compact disks and DVDs.

However, when the light-emitting elements and the light-detecting elements are integrated respectively for DVDs and compact disks, the optical integrated device tends to be complex in structure. The present invention has been made in view of the above shortcomings of the prior art, and provides an optical integrated device, an optical pickup, and an optical disk apparatus which are capable of accessing a plurality of types of optical disks with a simple arrangement.

It is an overall object of this invention therefore to provide an optical disk apparatus of the type described that is capable of accessing a plurality of types of optical disks with an uncomplicated arrangement.

To solve the above problems, the invention is applied to an optical integrated device, an optical pickup, or an optical disk apparatus. The optical integrated device comprises a first laser beam source for emitting a first laser beam having a first wavelength, a second laser beam source spaced a predetermined distance from the first laser beam source, for emitting a second laser beam having a second wavelength different from the first wavelength, a diffraction grating for dividing each of the feedback light corresponding to the first laser beam and the feedback light corresponding to the second laser beam into a plurality of rays, and a light-detecting element for commonly detecting the feedback light corresponding to the first laser beam and the feedback light corresponding to the second laser beam, with respect to at least a certain one of the rays divided by the diffraction grating.

According to the invention, the second laser beam source is spaced a predetermined distance from the first laser beam source, and the distance may be selected to divide the feedback light into a plurality of rays with the diffraction grating and detect feedback light corresponding to the first laser beam and feedback light corresponding to the second laser beam with the common light-detecting element, so that the overall structure can be simplified.

FIG. 1 is a schematic view of an optical system of the optical disk apparatus according to the embodiment of the invention.

FIG. 2 (A) is a cross-sectional view of an optical integrated device in an optical disk apparatus according to an embodiment of the invention, FIG. 2 (B) is a plan view of a light-detecting element in the embodiment of FIG. 2 (A); FIG. 2 (C) shows a pattern of hologram; and FIG. 2 (D) shows a relationship between FIGS. 2 (B) and 2 (C).

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of an optical system of an optical disk apparatus according to an embodiment of the present invention. The optical disk apparatus 1 plays back data recorded on an optical disk 2 B as a DVD and data recorded on an optical disk 2 A as a compact disk.

The compact disk 2 A is an optical disk comprising a transparent plate having a thickness of 1.2 mm where recorded data can be reproduced by processing feedback light produced when a laser beam is applied to an information-recorded surface of the optical disk through the transparent plate. The DVD 2 B is an optical disk comprising a transparent plate having a thickness of 0.6 mm where recorded data can be reproduced by processing feedback light produced when a laser beam is applied to an information-recorded surface of the optical disk through the transparent plate.

The optical disk apparatus 1 has an optical pickup 3 positioned so as to be movable radially of the optical disk by a typical sled mechanism. The optical pickup 3 operates by applying a laser beam emitted from an optical integrated device 4 through a collimator lens 5 , an aperture 6 , and an objective lens 7 to the optical disk 2 A or 2 B and applying feedback light coming from the optical disk 2 A or 2 B through the objective lens 7 , the aperture 6 , and the collimator lens 5 to the optical integrated device 4 .

The optical disk apparatus 1 processes the feedback light detected by the optical integrated device 4 to generate various signals required to play back the compact disk 2 A and the DVD 2 B. Based on a tracking error signal and a focus error signal among the generated signals, the optical disk apparatus 1 moves the objective lens 7 to effect tracking control and focusing control. The optical disk apparatus 1 processes a playback signal to reproduce data recorded on the optical disks 2 A, 2 B.

The optical integrated device 4 comprises a light-emitting element and a light-detecting element integrated into a single package, and is controlled by a system controller 10 to selectively emit a laser beam having a wavelength of 780 nm for use in playing back the compact disk 2 A and a laser beam having a wavelength of 650 nm for use in playing back the DVD 2 B. The optical integrated device 4 also detects feedback light produced upon application of the laser beam by the light-detecting element and outputs the detected feedback light.

The collimator lens 5 converts the laser beam emitted from the optical integrated device 4 into a substantially parallel beam, and emits the parallel beam.

The aperture 6 comprises a transparent plate having a dielectric film evaporated thereon with a central circular opening. The dielectric film surrounding the opening serves as a filter for selectively blocking light at 780 nm, which is the wavelength of the laser beam for the compact disk, and passing light at 650 nm, which is the wavelength of the laser beam for the DVD. The aperture 6 shapes and passes the laser beam for the compact disk according to a beam diameter determined by the opening, and passes the laser beam for the DVD without shaping its beam configuration.

The objective lens 7 comprises an aspheric plastic lens that has been injection-molded of a transparent synthetic resin. By selecting the refractive index of the transparent synthetic resin and the shapes of the lens surfaces, the objective lens 7 is capable of focusing the laser beam for the compact disk and the laser beam for the DVD, each applied as a parallel beam, onto the respective information-recorded surfaces of the corresponding optical disks 2 A, 2 B. The objective lens 7 thus serves as a bifocal lens for the laser beam for the compact disk and the laser beam for the DVD.

The objective lens 7 is movable radially of the optical disks 2 A, 2 B by a tracking control actuator which comprises a voice-coil motor. The tracking control is performed by energizing the tracking control actuator based on the tracking error signal. The objective lens 7 can also be moved along the optical axis of the laser beams by a similar actuator. The focusing control can be performed by energizing this actuator based on the focus error signal.

A matrix processor 9 effects matrix processing on the detected feedback light outputted from the optical integrated device 4 to generate a tracking error signal TE whose signal level varies depending on the tracking error, a focus error signal FE whose signal level varies depending on the focus error, and a playback signal RF whose signal level varies depending on the bit train.

FIG. 2 (A) is a cross-sectional view of the optical integrated device 4 taken along the radial direction of the optical disks 2 A, 2 B, and FIG. 2 (B) is a plan view of the light-detecting element of the optical integrated device. The optical integrated device 4 comprises semiconductor laser diode chips 15 A, 15 B mounted on a semiconductor substrate 17 . After the semiconductor substrate 17 is housed in a package and interconnections are made to the semiconductor substrate 17 , the assembly is sealed by lid glass 19 as a transparent sealing member into the optical integrated device 4 .

A light-detecting element 20 is mounted on the semiconductor substrate 17 . In the optical integrated device 4 , the semiconductor laser diode chips 15 A, 15 B and the light-detecting element 20 are juxtaposed in the radial direction of the optical disks 2 A, 2 B.

A plan view of the light-detecting element of FIG. 2A is shown in FIG. 2 B. The light-detecting element 20 has rectangular photodetector surfaces 20 A, 20 B juxtaposed in the radial direction (arrow R) of the optical disks 2 A, 2 B, and elongate rectangular photodetector surfaces 20 C, 20 D sandwiching the rectangular photodetector surfaces 20 A, 20 B therebetween and juxtaposed in a direction tangential (arrow T) to the optical disks 2 A, 2 B.

Of these photodetector surfaces 20 A to 20 D, the rectangular photodetector surface 20 A positioned closely to the semiconductor laser diode chips is divided into four cross-partitioned square photodetector surfaces A to D by parting lines extending in the radial (arrow R) and tangential (arrow T) directions of the optical disks 2 A, 2 B. The rectangular photodetector surface 20 A can output detected signals from the respective photodetector surfaces A to D.

The rectangular photodetector surface 20 B next to the rectangular photodetector surface 20 A is divided into two rectangular photodetector surfaces L, M by a parting line extending in the radial direction of the optical disks 2 A, 2 B. The rectangular photodetector surface 20 B can output detected signals from the respective photodetector surfaces L, M.

The lid glass 19 includes a hologram 19 A and a diffraction gating 19 B as a diffraction grating means. The diffraction grating 19 B is provided on one surface of the lid glass 19 so as to be opposite to the semiconductor laser diode chips 15 A, 15 B and diffracts laser beams LA and LB emitted toward the optical disks 2 A, 2 B and divides the laser beams LA and LB into 0, −1 and +1 orders of diffraction lights. The hologram 19 A is provided on the other surface of the lid glass 19 , and diffracts feedback light returned from the optical disks 2 A, 2 B to the photodetector surfaces 20 A to 20 D. The optical integrated device 4 applies the rays, which are diffracted by the diffraction grating 19 B, to the optical disks 2 A, 2 B. The light-detecting element 20 detects the rays, which are diffracted by the hologram 19 A, with the photodetector surfaces 20 A to 20 D.

FIG. 2 (C) is a pattern view of the hologram 19 A. The hologram 19 A comprises a first area 19 A 1 , a second area 19 A 2 and a third area 19 A 3 , having formed therein holographic gratings different in grating constant from each other, respectively. The feedback light of the laser beams LA and LB incident upon the hologram 19 A are diffracted at different angles, respectively, depending upon the grating constants of the holographic areas upon which the feedback light is incident, respectively.

FIG. 2 (D) shows a relationship between FIGS. 2 (B) and 2 (C). The 0-order feedback light incident on the first are 19 A 1 is diffracted so as to be received by the photodetector surface 20 A, at positions near to the semiconductor laser diode chips 15 A, 15 B. The +1-order feedback light and the −1-order feedback light incident on the first area 19 A 1 are diffracted so as to be received by the photodetector surface 20 E and 20 F, at positions near to the semiconductor laser diode chips 15 A, 15 B. The 0-order feedback light incident on the second area 19 A 2 is diffracted so as to be received by the photodetector surface 20 A, at positions farther from the semiconductor laser diode chips 15 A, 15 B. The +1-order feedback light and the −1-order feedback light incident on the second area 19 A 2 are diffracted so as to be received by the photodetector surface 20 E and 20 F, at positions near to the of the photodetector surface 20 E and 20 F. The 0-order feedback light incident on the third area 19 A 3 is diffracted so as to be received by the photodetector surface 20 B. The +1-order feedback light and the −1-order feedback light incident on the third area 19 A 3 are diffracted so as to be received by the photodetector surface 20 E and 20 F, at positions farther from the semiconductor laser diode chips 15 A, 15 B.

Specifically, the laser beam LA for the CD 2 A will be described below. When the optical integrated device 4 emits the laser beam LA to the optical disk 2 A, the diffraction grating 19 B divides the laser beam LA into 0, −1, and +1 orders of diffraction light, and emits the 0, −1, and +1 orders of diffraction light. The hologram 19 A applies feedback light of the 0-order diffraction light of those 0, −1, and +1 orders of diffraction light, to the photodetector surface 20 A and 20 B such that the feedback light of the 0-order diffraction light forms a beam spot SPA substantially centrally on the surfaces of the photodetectors 20 A and 20 B. The photodetectors 20 A and 20 B generate a playback signal (A+B+C+D+L+M) whose signal level varies depending on the bit train. The hologram 19 A focuses the −1-order diffraction light and the +1-order diffraction light respectively on the photodetector surfaces 20 C, 20 D that are positioned one on each side of the surfaces of the photodetectors 20 A and 20 B. The photodetectors 20 C and 20 D generate a tracking error signal according to a three-beam method (E-F). The photodetector 20 A generates a focus error signal according to the Foucault method, i.e. (A+D)−(B+C).

Also, the laser beam LB for the DVD 2 B will be described below. When the optical integrated device 4 emits the laser beam LB to the optical disc 2 B, the diffraction grating 19 B divides the laser beam LB into 0, −1, and +1 orders of diffraction light, and emits the 0, −1, and +1 orders of diffraction light. The hologram 19 A applies feedback light of the 0-order diffraction light, of those 0, −1, and +1 orders of diffraction light, to the photodetector surface 20 A and 20 B such that the feedback light of the 0-order diffraction light forms a beam spot SPB at substantially the same position of the beam spot SPA on the photodetector surfaces 20 A. The photodetectors 20 A and 20 B generate a playback signal (A+B+C+D+L+M) whose signal level varies depending on the bit train. Then, the photodetector 20 A and 20 B generates a tracking error signal according to the DPD (Differential Phase Detection) method.

The hologram 19 A focuses the −1-order diffraction light and the +1-order diffraction light respectively on the photodetector surfaces 20 C, 20 D that are positioned one on each side of the photodetector surface 20 A. However, the photodetectors 20 C and 20 D are not used for the optical disk 2 B. The photodetector 20 B generates a focus error signal according to the Foucault method, i.e. (A+D)−(B+C).

In the optical integrated device 4 , the semiconductor laser diode chips 15 A, 15 B are arranged such that the beam spot SPB of the laser beam LB for the DVD and the beam spot SPA of the laser beam LA for the compact disk have their centers aligned with each other on the four-segment photodetector surface 20 A. The diffraction angle θ of the feedback light emitted from the hologram 19 A, the wavelength λ of the feedback light, and the repetition pitch p of the hologram 19 A are basically related to each other according to the following equation:

λ= p ×sin θ  (1)

For example, if the repetition pitch p of the hologram 19 A is 4 μm, then the diffraction angle θA of the feedback light of the laser beam LA having the wavelength of 780 nm used to play back the compact disk 2 A is 11.24 degrees, whereas the diffraction angle θA of the feedback light of the laser beam LB having the wavelength of 650 nm used to play back the DVD 2 B is 9.35 degrees.

In the optical integrated device 4 , the semiconductor laser diode chip 15 A for the compact disk where the diffraction angles θA, θB are larger is located farther from the photodetector surface 20 A, and a light emission spot of the semiconductor laser diode chip 15 A for the compact disk and a light emission spot of the semiconductor laser diode chip 15 B for the DVD are spaced from each other by a given distance D. In the optical integrated device 4 , even though the diffraction angles θA, θB are different from each other, the distance D is selected such that the beam spot SPB of the feedback light of the laser beam LB for the DVD and the beam spot SPA of the feedback light of the laser beam LA for the compact disk have their centers substantially aligned with each other on the four-segment photodetector surface 20 A.

Though the distance D varies depending on the distance from the photodetector surface of the light-detecting element 20 , the design of the hologram 19 A, and so forth, the distance D has a practical range from 10 μm to 500 μm.

In the light-detecting element 20 , as indicated by beam spots SPA of the feedback light of the laser beam LA, the feedback light of the laser beam LA is focused on the photodetector surfaces 20 B to 20 D, other than the photodetector surface 20 A, at positions farther from the semiconductor laser diode chips 15 A, 15 B and the photodetector surface 20 A than focused positions of the feedback light of the laser beam LB for the DVD 2 B. In the light-detecting element 20 , the photodetector surfaces 20 C, 20 D and the remaining rectangular photodetector surface 20 B are formed so as to be capable of detecting the beam spots SPA focused at positions farther than the focused beam spots SPB of the laser beam LB for the DVD 2 B. With this arrangement, when the compact disk 2 A is accessed using the light-detecting element commonly used for accessing the DVD 2 B, a tracking error signal can be generated according to the push-pull method instead of the DPD method.

For playing back the DVD 2 B, the matrix processor 9 (FIG. 1) converts currents detected by the four-segment photodetector surface 20 A into voltages, and compares the phases of the converted voltages from the photodetector surfaces A+B closer to the semiconductor laser diode chips with each other and the photodetector surfaces C+D farther from the semiconductor laser diode chips with each other. Furthermore, the matrix processor converts currents detected by the two-segment photodetector surface 20 B into voltages, and compares the phases of the converted voltages from the photodetector surfaces L and M. The matrix processor 9 then generates a differential signal from the compared phases to generate a tracking error signal TE according to the DPD method.

The converted voltages from the photodetector surface 20 A are added to generate a playback signal RF represented by A+B+C+D using the photodetector surfaces A to D, and similarly to generate a focus error signal FE represented by (A+D)−(B+C).

For playing back the compact disk 2 A, the matrix processor 9 generates a playback signal RF and a focus error signal FE in the same manner as for playing back the DVD 2 B. The matrix processor 9 generates a differential signal from converted voltages from the photodetector surfaces F, E to generate a tracking error signal according to the three-beam method.

In the operation of the optical disk apparatus 1 (FIG. 1 ), the optical pickup 3 applies a laser beam to the optical disks 2 A, 2 B and detects feedback light. The signal processor processes the detected feedback light to reproduce information recorded on the optical disks 2 A, 2 B.

Specifically, the optical integrated device 4 in the optical pickup 3 emits a laser beam which is converted into an approximately parallel beam by the collimator lens 5 . The laser beam then passes through the aperture 6 to the objective lens 7 , which focuses the laser beam onto the information-recorded surfaces of the optical disks 2 A, 2 B. Feedback light produced when the laser beam is applied to the optical disks 2 A, 2 B is applied through the objective lens 7 to the optical integrated device 4 , which detects the feedback light.

In the optical disk apparatus 1 , a tracking error signal TE is generated from the detected feedback light. The objective lens 7 is moved in the radial direction of the optical disks 2 A, 2 B such that the tracking error signal TE has a predetermined signal level, for thereby performing tracking control. Similarly, a focus error signal FE is generated, and the objective lens 7 is moved in the vertical direction such that the focus error signal FE has a predetermined signal level, for thereby performing focus control.

In the above operation of the optical pickup, if the optical disk loaded in the optical disk apparatus 1 is the DVD 2 B, then of the semiconductor laser diode chips 15 A, 15 B (FIG. 2 (A)) juxtaposed in the radial direction (arrow R) of the optical disks 2 A, 2 B, the semiconductor laser diode chip 15 B for the DVD selectively emits the laser beam LB, and the laser beam LB is divided by the diffraction grating 19 B into three diffraction beams that are applied to the DVD 2 B. Feedback light from the DVD 2 B is divided by the hologram 19 A into a plurality of rays that are detected by the light-detecting element 20 .

The rays detected by the light-detecting element 20 are processed by the matrix processor 9 to generate a tracking error signal TE according to the DPD method, a focus error signal FE according to the Foucault method, and a playback signal RF whose signal level varies depending on the bit train on the DVD 2 B. Various items of information recorded on the DVD 2 B are reproduced based on the playback signal RF.

Conversely, if the compact disk 2 A is loaded in the optical disk apparatus 1 , then of the semiconductor laser diode chips 15 A, 15 B (FIG. 2 (A)), the semiconductor laser diode chip 15 A for the compact disk selectively emits the laser beam LA, and the laser beam LA is applied to the compact disk 2 A as is the case with the DVD 2 B. Feedback light from the compact disk 2 A is detected by the common light-detecting element 20 used for detecting the feedback light from the DVD 2 B.

For detecting the feedback light, the semiconductor laser diode chip 15 A for the compact disk 2 A is spaced from the light-detecting element 20 more remotely from the semiconductor laser diode chip 15 B for the DVD 2 B to bring the centers of the beam spots SPB, SPA for playing back the DVD 2 B and the compact disk 2 A, respectively, into substantial agreement with each other on the four-segment photodetector surface 20 A while compensating for the difference between the diffraction angles θA, θB of the hologram 19 A. This arrangement allows the single light-detecting element 20 to detect feedback light from the optical disks 2 A, 2 B which are of different types.

Specifically, the compact disk 2 A and the DVD 2 B are characterized in that the wavelengths of laser beams used to play back them are different from each other, and different methods are employed to generate a tracking error signal TE due to different pit depths.

In the optical disk apparatus 1 , the optical integrated device 4 is simplified in construction. The optical disk apparatus 1 is thus simplified in overall structure, and is capable of accessing optical disks of plural types.

There are significant advantages with the device according to the invention. With the above arrangement, laser sources having different wavelengths are spaced a predetermined distance from each other in order to compensate for the difference between the diffraction angles of a diffraction grating, so that feedback light produced by the laser sources having different wavelengths can be detected by a common light-emitting element. An optical integrated device, an optical pickup, and an optical disk apparatus can be simplified in construction and are capable of accessing optical disks of plural types.

In the above embodiment, the semiconductor laser diode chips 15 A, 15 B and the light-detecting element 20 are juxtaposed in the radial direction of the optical disks 2 A, 2 B. However, the semiconductor laser diode chips 15 A, 15 B and the light-detecting element 20 may be juxtaposed in a direction tangential to the optical disks.

In the above embodiment, the objective lens comprises a bifocal lens. The present invention is not limited to such a lens, but a dual-wavelength hologram may be formed on a surface of the objective lens to handle different wavelengths, or various other focusing means for focusing laser beams having different wavelengths may be employed.

In the above embodiment, a tracking error signal is generated according to the DPD method and the three-beam method, and a focus error signal is generated according to the Foucault method. The present invention is not limited to those methods, but various other methods may be employed to generate a tracking error signal and a focus error signal.

In the above embodiment, detected signals from the four-segment photodetector surface 20 A are added to generate a playback signal. The present invention is not limited to such a process of generating a playback signal, but various other processes of generating a playback signal may be employed. For example, detected signals from the other photodetector surface 20 B, etc. may be used to generate a playback signal, and detected signals from the other photodetector surface 20 B, etc. and detected signals from the photodetector surface 20 A may be added to generate a playback signal.

In the above embodiment, the semiconductor laser diode chips 15 A, 15 B are spaced at the distance D from each other on the semiconductor substrate 17 . The present invention is not limited to such a structure, but a plurality of laser diodes having different wavelengths may be integrated on a single semiconductor chip. In this case, since the accuracy of the layout can be increased depending on the distance D, and hence the yield can be increased and the optical integrated device can be reduced in size.

In the above embodiment, the compact disk and the DVD are played back. The present invention is not limited to the playback of those disks, but may be applied to accessing the compact disk and the CD-R, for example.

In the above embodiment, accessing two types of optical disks has been described. The present invention is not limited to two types of optical disks, but may be applied to accessing a plurality of types of optical disks.

According to the present invention, as described above, for dividing feedback light with the diffraction grating and detecting the divided feedback light with the light-detecting element, the laser sources having different wavelengths are spaced a predetermined distance from each other in order to compensate for the difference between the diffraction angles of the diffraction grating. In this manner, the light-detecting element is used in common, and a plurality of types of optical disks can be accessed with a simple arrangement.