This nonprovisional application claims priority under 35 U.S.C. ยง119(a) on Patent Application No(s). 2006-311639 filed in Japan on Nov. 17, 2006, the entire contents of which are hereby incorporated by reference.
The present invention relates to an optical pickup device which optically records information on and reproduces the information from a disc-shaped recording medium.
As optical discs for optical reading of signals with use of light beams such as laser beams, CDs (Compact Discs) which have the thickest transparent cover at the side of signal reading (light incidence side) and which are adapted for recording and reproduction of information with use of a light source emitting infrared laser beams are popular. In response to the needs for higher capacity, high density discs which have the same disc diameter as CDs to ensure structural compatibility and which further support recording in density higher than CDs to achieve higher capacity have been proposed. These discs include DVDs (Digital Versatile Discs) which have the transparent cover at the side of signal reading thinner than that of the CDs and which are adapted for recording and reproduction of information with use of a light source emitting red laser beams, super high density BDs (Blu-ray Discs) which have the transparent cover at the side of signal reading thinner than that of the DVDs and which are adapted for recording and reproduction of information with use of a light source which emits blue-violet laser beams having shorter wavelengths, and HD-DVDs (High Definition DVDs) which have the transparent cover at the side of signal reading (light incidence side) thinner than that of the CDs and thicker than that of the BDs, and which are adapted for recording and reproduction of information with use of a light source emitting blue-violet laser beams.
In order to enable optical pickup devices to read three kinds of signals different in wavelengths, that is, signals from CDs, DVDs which are high-density discs, and BDs or HD-DVDs which are super-high-density discs, laser diodes which emit light beams in three kinds of wavelengths and optical systems which support three kinds of wavelengths are necessary, and therefore it is required to switch the light sources and the optical systems for use in response to the recording density of recording media subjected to signal reading. For example, the pickups, which support three kinds of discs, including BDs, DVDs and CD, as well as HD-DVDs, DVDs and CDs, can be structured by taking advantage of the point that three kinds of wavelengths in use are different from each other (e.g., JP 2005-353259 A, JP 2005-353250 A, and JP 2006-40411 A).
However, the conventional optical pickups structured by taking advantage of the point that three kinds of wavelengths in use are different from each other have the following problems.
That is, the BDs and the HD-DVDs subject to use of blue-violet laser having the shortest wavelength are different in the thickness of the transparent cover layer at the side of the signal reading (light incidence side) in the optical disc, so that it is difficult to record information on and to reproduce information from the BDs and the HD-DVDs by the same optical pickup. In short, it is difficult to record information on and to reproduce information from all the discs including CDs, DVDs, HD-DVDs and BDs with the same optical pickup.
Accordingly, it is necessary to prepare separate optical pickups, an optical pickup corresponding to BDs (DVDs, CDs), and an optical pickup corresponding to HD-DVDs (DVDs, CDs), and therefore two drive devices are necessary for performing recording and reproduction operation in both the BDs and the HD-DVDs. This causes a problem of increase in size and costs of the entire product.
An object of the present invention is to provide an optical pickup which can record information on and reproduce information from four kinds of discs with three wavelengths, or an optical pickup which can record information on and reproduce information from both the BDs and the HD-DVDs.
In order to achieve the above object, there is provided an optical pickup device, comprising:
a first light source for emitting a first wavelength laser beam to a disc-shaped first recording medium which is subjected to recording and reproduction of information with the first wavelength laser beam;
a second light source for emitting a second wavelength laser beam to a disc-shaped second recording medium which is subjected to recording and reproduction of information with the second wavelength laser beam;
a third light source for emitting a third wavelength laser beam to a disc-shaped third recording medium which is subjected to recording and reproduction of information with the third wavelength laser beam and to a disc-shaped fourth recording medium which is subjected to recording and reproduction of information with the third wavelength laser beam;
a first optical system for guiding the first wavelength laser beam emitted from the first light source to the first recording medium;
a second optical system for guiding the second wavelength laser beam emitted from the second light source to the second recording medium;
a polarization beam splitter having a polarization beam splitting function for splitting the third wavelength laser beam and a dichroic function with wavelength selectivity for the first wavelength laser beam and the second wavelength laser beam, the polarization beam splitter splitting an optical path of the third wavelength laser emitted from the third light source into a first optical path going to the third recording medium and a second optical path going to the fourth recording medium; and
a polarizing orientation switchover element which is placed on an optical axis between the third light source and the polarization beam splitter for rotating a polarization direction of the third wavelength laser beam emitted from the third light source 90 degrees, and splitting a luminous flux of the third wavelength laser beam into either the first optical path or the second optical path with the polarization beam splitter, wherein with light beams of three wavelengths including the first wavelength laser beam from the first light source, the second wavelength laser beam from the second light source and the third wavelength laser beam from the third light source, information can be recorded on and reproduced from four kinds of disc-shaped recording media including the first recording medium, the second recording medium, the third recording medium and the fourth recording medium.
According to the above structure, the optical pickup device includes a polarization beam splitter having a polarization beam splitting function for splitting the third wavelength laser beam, and a dichroic function with wavelength selectivity for the first wavelength laser beam and the second wavelength laser beam, for splitting the optical path of the third wavelength laser from the third light source into a first optical path and a second optical path, and a polarizing orientation switchover element for rotating the polarization direction of the third wavelength laser beam from the third light source 90 degrees so that the polarization beam splitter splits the optical path of the third wavelength laser beam into either the first optical path side or the second optical path side. Consequently, depending on the use and non-use of the polarizing orientation switchover element, it becomes possible to record information on and reproduce information from the fourth recording medium with the thinnest transparent cover at the side of signal reading and the third recording medium with the transparent cover at the side of signal reading thicker than that of the fourth recording medium with use of one wavelength of the third wavelength laser beam from the third light source.
Therefore, by using the first optical system for guiding the first wavelength laser beam emitted from the first light source to the first recording medium having the thickest transparent cover at the side of signal reading in combination with the second optical system for guiding the second wavelength laser beam emitted from the second light source to the second recording medium having the transparent cover at the side of signal reading thinner than that of the first recording medium, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
In one embodiment of the invention, the optical pickup device further comprises a polarizing orientation switchover element moving mechanism which inserts and extracts the polarizing orientation switchover element.
According to this embodiment, the polarizing orientation switchover element is inserted into and extracted from between the third light source and the polarization beam splitter by the polarizing orientation switchover element moving mechanism depending on which recording medium, the third recording medium or the fourth recording medium, is subjected to information recording and reproduction, so that with one wavelength of the third wavelength laser beam from the third light source, information can be recorded on and reproduced from the fourth recording medium with the thinnest transparent cover at the side of signal reading and the third recording medium with the transparent cover at the side of signal reading thicker than that of the fourth recording medium.
In one embodiment of the invention, the optical pickup device further comprises a plate glass or a transparent plate resin which is placed on an optical axis between the third light source and the polarization beam splitter, and which has a thickness optically equivalent to the polarizing orientation switchover element, and a plate moving mechanism for extractably inserting the plate glass or the transparent plate resin into a position where the polarizing orientation switchover element was present between the third light source and the polarization beam splitter after the polarizing orientation switchover element is extracted from the position blocking the optical axis.
According to this embodiment, a plate glass or a plate resin is extractably inserted into the position where the polarizing orientation switchover element was present, after the polarizing orientation switchover element is extracted from the position which blocks the optical axis between the third light source and the polarization beam splitter, so that a stable and sufficient condensing spot can be obtained regardless of the presence of the polarizing orientation switchover element without changing the designed thickness of the cover glass of, for example, a collimate lens.
In one embodiment of the invention, the polarizing orientation switchover element is inserted by the polarizing orientation switchover element moving mechanism into a position blocking the optical axis between the third light source and the polarization beam splitter so as to rotate a polarization direction of the third wavelength laser beam emitted from the third light source 90 degrees, the polarization beam splitter splits the third wavelength laser beam with the polarization direction rotated 90 degrees by the polarizing orientation switchover element into the second optical path side which goes to the fourth recording medium, and the optical pickup device comprises an objective lens for the fourth recording medium for guiding a luminous flux of the third wavelength laser beam split to the second optical path side by the polarization beam splitter to the fourth recording medium, so that with the third wavelength laser beam emitted from the third light source, information is recorded on and reproduced from the fourth recording medium.
According to this embodiment, the polarization direction of the third wavelength laser beam emitted from the third light source as, for example, a P wave toward the polarization beam splitter is rotated 90 degrees by the polarizing orientation switchover element inserted in between the third light source and the polarization beam splitter, so that the third wavelength laser beam is made to come incident into the polarization beam splitter as an S wave. The luminous flux of the third wavelength laser beam reflected by the polarization beam splitter and split from the first optical path is guided to the fourth recording medium through the objective lens, so that stable splitting characteristics can be obtained by making the polarization beam splitter reflect the S wave.
In one embodiment of the invention, the polarizing orientation switchover element is extracted by the polarizing orientation switchover element moving mechanism from a position blocking the optical axis between the third light source and the polarization beam splitter so as to prevent a polarization direction of the third wavelength laser beam emitted from the third light source from changing, the polarization beam splitter splits the third wavelength laser beam with the polarization direction unchanged by the polarizing orientation switchover element into the first optical path side which goes to the third recording medium, and the optical pickup device comprises an objective lens for the third recording medium for guiding a luminous flux of the third wavelength laser beam split to the first optical path side by the polarization beam splitter to the third recording medium, so that with the third wavelength laser beam emitted from the third light source, information is recorded on and reproduced from the third recording medium.
According to this embodiment, the polarizing orientation switchover element is removed from between the third light source and the polarization beam splitter. Consequently, the third wavelength laser beam emitted from the third light source toward the polarization beam splitter, for example, as a P wave is made to come incident into the polarization beam splitter without changing its polarization direction, and the luminous flux of the third wavelength laser beam which passed through the polarization beam splitter and was split into the first optical path is guided to the third recording medium through the objective lens, so that stable splitting characteristics can be obtained by making the polarization beam splitter transmit the P wave.
In one embodiment of the invention, the polarizing orientation switchover element is extracted by the polarizing orientation switchover element moving mechanism from a position blocking the optical axis between the third light source and the polarization beam splitter so as to prevent a polarization direction of the third wavelength laser beam emitted from the third light source from changing, the polarization beam splitter splits the third wavelength laser beam with the polarization direction unchanged by the polarizing orientation switchover element into the second optical path side which goes to the fourth recording medium, and the optical pickup device comprises an objective lens for the fourth recording medium for guiding a luminous flux of the third wavelength laser beam split to the second optical path side by the polarization beam splitter to the fourth recording media, so that with the third wavelength laser beam emitted from the third light source, information is recorded on and reproduced from the fourth recording medium.
According to this embodiment, the polarizing orientation switchover element is removed from between the third light source and the polarization beam splitter. Consequently, the third wavelength laser beam emitted from the third light source, for example, as a P wave toward the polarization beam splitter is made to come incident into the polarization beam splitter without changing its polarization direction, and the luminous flux of the third wavelength laser beam which was reflected by the polarization beam splitter and split into the second optical path is guided to the fourth recording medium through the objective lens, so that stable splitting characteristics can be obtained by making the polarization beam splitter reflect the P wave.
In one embodiment of the invention, the polarizing orientation switchover element is inserted by the polarizing orientation switchover element moving mechanism into a position blocking the optical axis between the third light source and the polarization beam splitter so as to rotate a polarization direction of the third wavelength laser beam emitted from the third light source 90 degrees, the polarization beam splitter splits the third wavelength laser beam with the polarization direction rotated 90 degrees by the polarizing orientation switchover element into the first optical path side which goes to the third recording medium, and the optical pickup device comprises an objective lens for the third recording medium for guiding a luminous flux of the third wavelength laser beam split to the first optical path side by the polarization beam splitter to the third recording medium, so that with the third wavelength laser beam emitted from the third light source, information is recorded on and reproduced from the third recording medium.
According to this embodiment, the polarization direction of the third wavelength laser beam emitted from the third light source as, for example, a P wave toward the polarization beam splitter is rotated 90 degrees by the polarizing orientation switchover element inserted in between the third light source and the polarization beam splitter, so that the third wavelength laser beam is made to come incident into the polarization beam splitter as an S wave. The luminous flux of the third wavelength laser beam which passed through the polarization beam splitter and was split into the first optical path is guided to the third recording medium through the objective lens, so that stable splitting characteristics can be obtained by making the polarization beam splitter transmit the S wave.
In one embodiment of the invention, the first wavelength laser beam from the first light source is an infrared laser beam, the second wavelength laser beam emitted from the second light source is a red laser beam, and the third wavelength laser beam emitted from the third light source is a blue-violet laser beam.
According to this embodiment, the infrared laser beam with the longest wavelength is emitted from the first light source, the red laser beam with a medium wavelength is emitted from the second light source, and the blue-violet laser beam with the shortest wavelength is emitted from the third light source. Therefore, with the light beams of three wavelengths including the infrared laser beam, the red laser beam, and the blue-violet laser beam, information can be recorded on and reproduced from the four kinds of disc-shaped recording media.
Also, there is provided an optical pickup device, comprising:
a light source for emitting a blue-violet laser beam to a disc-shaped first recording medium which is subjected to recording and reproduction of information with the blue-violet laser beam and to a disc-shaped second recording medium which is subjected to recording and reproduction of information with the blue-violet wavelength laser beam;
a first objective lens for guiding the blue-violet laser beam emitted from the light source to the first recording medium;
a second objective lens for guiding the blue-violet laser beam emitted from the light source to the second recording medium;
a half mirror for splitting the blue-violet laser beam emitted from the light source into a first optical path in which the blue-violet laser beam passes toward the first objective lens side, and a second optical path in which the blue-violet laser beam is reflected toward the second objective lens; and
a reflective mirror for reflecting the blue-violet laser beam split to the first optical path side by the half mirror toward the first objective lens,
wherein with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from two kinds of disc-shaped recording media including the first recording medium and the second recording medium.
According to the structure, the blue-violet laser beam emitted from the light source is split by the half mirror to the first optical path in which the blue-violet laser beam passes toward the first objective lens and to the second optical path in which the blue-violet laser beam is reflected toward the second objective lens, and the blue-violet laser beam reflected toward the second objective lens is guided to the second recording medium via the second objective lens, while the blue-violet laser beam which passed toward the first objective lens is reflected by the reflective mirror toward the first objective lens side and is guided to the first recording medium via the first objective lens, so that with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from the first recording medium having the thinnest transparent cover at the side of signal reading and the second recording medium with the transparent cover at the side of signal reading thicker than that of the first recording medium.
Therefore, by using the first optical system for guiding the infrared laser beam emitted from the second light source to the third recording medium having the thickest transparent cover at the side of signal reading and the second optical system for guiding the red laser beam emitted from the third light source to the fourth recording medium having the transparent cover at the side of signal reading thinner than that of the third recording medium in combination with the above optical pickup device including the light source for emitting the blue-violet laser beam, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
Also, there is provided an optical pickup device, comprising:
a light source for emitting a blue-violet laser beam to a disc-shaped first recording medium which is subjected to recording and reproduction of information with the blue-violet laser beam and to a disc-shaped second recording medium which is subjected to recording and reproduction of information with the blue-violet wavelength laser beam;
a first objective lens for guiding the blue-violet laser beam emitted from the light source to the first recording medium;
a second objective lens for guiding the blue-violet laser beam emitted from the light source to the second recording medium;
a half mirror for splitting the blue-violet laser beam emitted from the light source into a first optical path in which the blue-violet laser beam passes toward the second objective lens side, and a second optical path in which the blue-violet laser beam is reflected toward the first objective lens; and
a reflective mirror for reflecting the blue-violet laser beam split to the first optical path side by the half mirror toward the second objective lens,
wherein with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from two kinds of disc-shaped recording media including the first recording medium and the second recording medium.
According to the structure, the blue-violet laser beam emitted from the light source is split by the half mirror to the first optical path in which the blue-violet laser beam passes toward the second objective lens and to the second optical path in which the blue-violet laser beam is reflected toward the first objective lens, and the blue-violet laser beam reflected toward the first objective lens is guided to the first recording medium via the first objective lens, while the blue-violet laser beam which passed toward the second objective lens is reflected by the reflective mirror toward the second objective lens side and is guided to the second recording medium via the second objective lens, so that with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from the first recording medium having the thinnest transparent cover at the side of signal reading and the second recording medium with the transparent cover at the side of signal reading thicker than that of the first recording medium.
Therefore, by using the first optical system for guiding the infrared laser beam emitted from the second light source to the third recording medium having the thickest transparent cover at the side of signal reading and the second optical system for guiding the red laser beam emitted from the third light source to the fourth recording medium having the transparent cover at the side of signal reading thinner than that of the third recording medium in combination with the above optical pickup device including the light source for emitting the blue-violet laser beam, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
In one embodiment of the invention, the first objective lens is an objective lens dedicated for the first recording medium, and the second objective lens is a diffractive object lens which can support the second recording medium, a disc-shaped third recording medium which has a thickest transparent cover at a side of signal reading and which is subjected to recording and reproduction of information with a infrared laser beam, and a disc-shaped fourth recording medium which has a transparent cover at a side of signal reading thinner than that of the third recording medium and which is subjected to recording and reproduction of information with a red laser beam.
According to this embodiment, since the second objective lens is constituted from a diffractive object lens which can support the third recording medium and the fourth recording medium in addition to the second recording medium, when this diffractive object lens is included as a constituent of the first optical system for guiding the infrared laser beam emitted from the second light source to the third recording medium and the second optical system for guiding the red laser beam emitted from the third light source to the fourth recording medium, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with light beams of three wavelengths with a low cost structure without needing a complicated mechanism.
In one embodiment of the invention, when a recording medium which is a destination of the blue-violet laser beam reflected by the half mirror is a recording medium for reproduction only and the other recording medium is a recording medium for reproduction and recording, the half mirror is so set that reflectance is lower than transmittance, and when a recording medium which is a destination of the blue-violet laser beam reflected by the half mirror is a recording medium for reproduction and recording and the other recording medium is a recording medium for reproduction only, the half mirror is so set that reflectance is higher than transmittance.
According to this embodiment, when one of two recording media, which are destinations of two optical paths split by the half mirror, is a recording medium for reproduction only, the quantity of the light beam split to the optical path leading to the recording medium for both reproduction and recording is increased, which makes it possible to avoid applying load on the laser power of the light source, and to accomplish the optical pickup device with less energy consumption.
As is clear from the above, the optical pickup device of the present invention has a polarizing orientation switchover element which is placed between the third light source and the polarization beam splitter for splitting the optical path of the third wavelength laser from the third light source into a first optical path and a second optical path, and which rotates the polarization direction of the third wavelength laser beam from the third light source 90 degrees. Consequently, depending on the use and non-use of the polarizing orientation switchover element, information can be recorded on and reproduced from the fourth recording medium and the third recording medium which are different in the thickness of the transparent cover at the side of signal reading with one wavelength of the third wavelength laser beam from the third light source.
Therefore, by using the first optical system for guiding the first wavelength laser beam emitted from the first light source to the first recording medium having the thickest transparent cover at the side of signal reading and the second optical system for guiding the second wavelength laser beam emitted from the second light source to the second recording medium having the transparent cover at the side of signal reading thinner than that of the first recording medium in combination with the above optical pickup device including the third light source, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
Also in the optical pickup device of the present invention, the blue-violet laser beam emitted from the light source is split by the half mirror to the first optical path in which the blue-violet laser beam passes toward the first objective lens and to the second optical path in which the blue-violet laser beam is reflected toward the second objective lens, and the blue-violet laser beam which passed toward the first objective lens is reflected by the reflective mirror toward the first objective lens, so that with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from the first recording medium having the thinnest transparent cover at the side of signal reading and the second recording medium having the transparent cover at the side of signal reading thicker than that of the first recording medium.
Therefore, by using the first optical system for guiding the infrared laser beam emitted from the second light source to the third recording medium having the thickest transparent cover at the side of signal reading and the second optical system for guiding the red laser beam emitted from the third light source to the fourth recording medium having the transparent cover at the side of signal reading thinner than that of the third recording medium in combination with the above optical pickup device including the light source for emitting the blue-violet laser beam, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
Also in the optical pickup device of the present invention, the blue-violet laser beam emitted from the light source is split by the half mirror to the first optical path in which the blue-violet laser beam passes toward the second objective lens and to the second optical path in which the blue-violet laser beam is reflected toward the first objective lens, and the blue-violet laser beam which passed toward the second objective lens is reflected by the reflective mirror toward the second objective lens, so that with one wavelength of the blue-violet laser beam from the light source, information can be recorded on and reproduced from the first recording medium having the thinnest transparent cover at the side of signal reading and the second recording medium having the transparent cover at the side of signal reading thicker than that of the first recording medium.
Therefore, by using the first optical system for guiding the infrared red laser beam emitted from the second light source to the third recording medium having the thickest transparent cover at the side of signal reading and the second optical system for guiding the red laser beam emitted from the third light source to the fourth recording medium having the transparent cover at the side of signal reading thinner than that of the third recording medium in combination with the above optical pickup device including the light source emitting the blue-violet laser beam, it becomes possible to record information on and reproduce information from four kinds of disc-shaped recording media with use of light beams of three wavelengths.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not intended to limit the present invention, and wherein:
Hereinbelow, the present invention will be described in details in conjunction with the embodiments with reference to the drawings.
In
The circularly polarized beam reflected from the BD disc 12, which has the rotation direction reverse to the direction before the reflection, is converted to a linearly polarized beam by the quarter-wave plate 9, and comes incident into the blue-violet PBS 7 as a P wave. Herein, the direction of the linearly polarized beam in this case is different from the direction of the original linearly polarized beam (at the time of incident) by 90 degrees. Then, the light beam which was incident into the blue-violet PBS 7 passes through the blue-violet PBS 7, the red PBS 6 and the infrared PBS 5, before going to a cylindrical lens 13, where a focus error signal is generated, and to a light receiving element 14, where an RF signal, a tracking error signal and a focus error signal are detected.
The circularly polarized beam reflected from the HD-DVD disc 18a, which has the rotation direction reverse to the direction before the reflection, is converted to a linearly polarized beam by the quarter-wave plate 15, and comes incident into the blue-violet PBS 7 as an S wave. It is to be noted that the direction of the linearly polarization in this case is different from the direction of the original linearly polarized beam (at the time of incident) by 90 degrees. Then, the light beam which was incident into the blue-violet PBS 7 is reflected by the blue-violet PBS 7, and passes through the red PBS 6 and the infrared PBS 5, before going to a cylindrical lens 13, where a focus error signal is generated, and to a light receiving element 14, where an RF signal, a tracking error signal and a focus error signal are detected.
The reason why the luminous flux is guided to both the HD-DVD disc 18a and the DVD disc 18b by the same diffractive object lens 17 is because the thickness of the protective layer in both the HD-DVD disc 18a and the DVD disc 18b is about 0.6 mm, and so the diffractive object lens 17 can be designed easily. As a result, in the present embodiment, only the objective lens 11 can be set as a lens dedicated for BDs, while a common diffractive object lens 17 can be used for other discs including HD-DVDs, DVDs and CDs.
Further, as with the case of the HD-DVD, the reflected light beam from the DVD disc 18b with the rotation direction of being reverse to the direction before the reflection is converted from the circularly polarized beam into a linearly polarized beam by the quarter-wave plate 15, and comes incident into the blue-violet PBS 7 as an S wave. It is to be noted that the direction of the linearly polarization in this case is different from the direction of the original linearly polarized beam (at the time of incident) by 90 degrees. Then, the light beam which was incident into the blue-violet PBS 7 is reflected by the blue-violet PBS 7, and passes through the red PBS 6 and the infrared PBS 5, before going to a cylindrical lens 13, where a focus error signal is generated, and to a light receiving element 14, where an RF signal, a tracking error signal and a focus error signal are detected.
Further, as with the case of the HD-DVD, the reflected light beam from the CD disc 18c with the rotation direction of the circularly polarized beam being reverse to the direction before the reflection is converted from the circularly polarized beam into a linearly polarized beam by the quarter-wave plate 15, and comes incident into the blue-violet PBS 7 as an S wave. It is to be noted that the direction of the linearly polarization in this case is different from the direction of the original linearly polarized beam (at the time of incident) by 90 degrees. Then, the light beam which was incident into the blue-violet PBS 7 is reflected by the blue-violet PBS 7, and passes through the red PBS 6 and the infrared PBS 5, before going to a cylindrical lens 13, where a focus error signal is generated, and to a light receiving element 14, where an RF signal, a tracking error signal and a focus error signal are detected.
As is described above, in the present embodiment, the half-wave plate 4 can be inserted into and extracted from the luminous flux between the blue-violet laser emitting device 3 and the blue-violet PBS 7 depending on the BD disc 12 and the HD-DVD disc 18a. Therefore, the polarization direction of the emitted light from the blue-violet laser emitting device 3 can be changed by the insertion and extraction of the half-wave plate 4, so that the blue-violet PBS 7 can split the emitted light into the optical path which goes to the BD disc 12 and the optical path which goes to the HD-DVD disc 18a. In this way, write or read access of a signal to the BD disc 12 and the HD-DVD disc 18a can be performed with use of only one blue-violet laser emitting device 3.
The blue-violet PBS 7 has a dichroic function for infrared and red colors. Therefore, the blue-violet PBS 7 in combination with the half-wave plate 4 which can be inserted into and extracted from the luminous flux coming from the blue-violet laser emitting device 3 allows the same three-wavelength optical pickup device to record information on and reproduce information from all the discs of CDs, DVDs, HD-DVDs, and BDs.
Moreover, if the plate glass or the plate resin 4 having a thickness optically equivalent to the half-wave plate 4 is simultaneously inserted when the half-wave plate 4 is removed from the luminous flux coming from the blue-violet laser emitting device 3, a stable and sufficient condensing spot can be obtained regardless of the presence of the half-wave plate 4 without changing the designed thickness (i.e., aberration correction amount) of the cover glass of the collimate lens 16.
In that case, any appropriate structure can be used for the half-wave plate moving mechanism (not shown) which inserts and extracts the half-wave plate 4 and the plate moving mechanism (not shown) which inserts and extracts the plate glass or plate resin 4a. For example, the mechanisms may be structured so that when it is detected that the BD disc 12 has been loaded, the plate glass or plate resin 4a is extracted by the plate moving mechanism while the half-wave plate 4 is inserted by the half-wave plate moving mechanism, whereas when it is detected that the HD-DVD disc 18a has been loaded, the half-wave plate 4 is extracted by the half-wave plate moving mechanism while the plate glass or plate resin 4a is inserted by the plate moving mechanism.
Moreover, the luminous flux emitted from the blue-violet laser emitting device 3, which is a P wave relative to the blue-violet PBS 7, is subjected to 90 degree rotation of its polarization direction by the half-wave plate 4 so that it is incident into the blue-violet PBS 7 as an S wave, and is reflected by the PBS surface of the blue-violet PBS 7. Further, the luminous flux emitted from the blue-violet laser emitting device 3, which is a P wave relative to the blue-violet PBS 7, is made incident into the blue-violet PBS 7 as a P wave without changing the polarization direction, so that it passes through the blue-violet PBS 7 as a P wave. In this way, the stable splitting characteristics by the blue-violet PBS 7 can be achieved by making the blue-violet PBS 7 reflect an S wave while making the blue-violet PBS 7 transmit a P wave.
It is to be noted that in the present embodiment, the direction of the linearly polarization of the emitted light from the blue-violet laser emitting device 3 is so set as to be the P wave relative to the blue-violet PBS 7. However, the present invention is not limited to this setting and so the direction of the linearly polarization of emitted light can be so set as to be the S wave relative to the blue-violet PBS 7. However, in that case, the extraction and insertion of the half-wave plate 4 regarding BDs and HD-DVDs need to be reversed from those in
Further, the reflected light beam from the BD disc 12 is made incident into the blue-violet PBS 7 through the route reverse to the previous route, and the light beam which passed through the blue-violet PBS 7 then passes through the red PBS 6 and the infrared PBS 5, before being incident into the cylindrical lens 13.
Further, the reflected light beam from the HD-DVD disc 18a is incident into the blue-violet PBS 7 through the route reverse to the previous route, and the light beam reflected by the blue-violet PBS 7 then passes through the red PBS 6 and the infrared PBS 5, before being incident into the cylindrical lens 13.
The operation involving DVDs and CDs is also performed according to the operation involving HD-DVDs shown in
Thus, in the present embodiment, the parallel beam which passed through the collimate lenses 10 and 16 is reflected at generally right angles by the rising mirrors 21 and 22, respectively. Therefore, when the BD disc 12 and the HD-DVD, DVD, and CD discs 18a, 18b and 18c are horizontally placed, the height of the optical pickup device of the present embodiment is defined by the height of the rising mirror 21 (or the rising mirror 22), and the thickness of the objective lens 11 (or the diffractive object lens 17). Therefore, the height can be made sufficiently small as compared with the height of the optical pickup device of the first embodiment which is defined by the height of the total reflection mirror 8, the thickness of the quarter-wave plate 9, the thickness of the collimate lens 10 and the thickness of the objective lens 11.
In this case, the rising mirror 21 and the rising mirror 22 do not have polarization characteristics and therefore have transmission and reflection characteristics unaffected by the polarization direction. Consequently, even if the rising mirrors 21 and 22 are inserted, completely the same optical property as in the case of the first embodiment can be presented.
As a result, according to the present embodiment, it becomes possible to reduce the thickness of the optical pickup device.
Further, the reflected light beam from the DVD disc 18b is made incident into the blue-violet PBS 7 through a route reverse to the previous route, and the light beam reflected by the blue-violet PBS 7 passes through the red PBS 6 and comes incident into the cylindrical lens 13, where a focus error signal is generated. Then, the light beam is guided by the diffractive coaxial element 32 to the light receiving element 14, where an RF signal, a tracking error signal and a focus error signal are detected.
In the operation involving CDs, a luminous flux emitted from an infrared laser 31a in the two-wavelength laser emitting device 31 is reflected by the red PBS 6 and then operates in a way similar to the case involving DVDs described above. Moreover, the operation corresponding to BDs and HD-DVDs is similar to the operation as in the case of the second embodiment.
Thus, in the present embodiment, the two-wavelength laser emitting device 31 incorporating the infrared laser 31a and red laser 31b is used. Therefore, in the present embodiment, the infrared laser emitting device 1 and the infrared PBS 5 can be removed, so that reduction in parts count and high-reliability can be achieved.
In
In the above structure, in the case of recording information on and reproducing information from BD discs, as shown in
In the case of recording information on and reproducing information from HD-DVD discs, as shown in
As described above, in the present embodiment, the luminous flux is made to rise by the half mirror 44 and the total reflection mirror 45. Therefore, as with the case of the second embodiment, it becomes possible to reduce the thickness of the optical pickup device. Further, since the blue-violet hologram laser emitting device 41 having the blue-violet laser 41a, the light receiving element 41b and the hologram element 41c is used, it is not necessary to individually provide a blue-violet laser emitting device and a light receiving element. Therefore, the part count can be reduced to simplify the structure.
It is to be noted that in the above structure, the arrangement of the objective lens 46 for the BD disc 48 and the diffractive object lens 47 for the HD-DVD discs 49a can be exchanged. In that case, the installed position of the BD disc 48 and the HD-DVD disc 49a is also reversed. The arrangement of the objective lens 46 and the diffractive object lens 47 should appropriately be selected corresponding to the structure of the actuator in the optical pickup device. In that case, any arrangements can provide the optical pickup device having simplified structure.
As shown in
In the above structure, in the case of recording information on and reproducing information from BD discs, as shown in
In the case of recording information on and reproducing information from HD-DVD discs, as shown in
In the case of recording information on and reproducing information from CD discs, as shown in
In the case of recording information on and reproducing information from DVD discs, as shown in
As mentioned above, according to the present embodiment, the red and infrared two-wavelength hologram laser emitting device 51, the blue-violet hologram laser emitting device 53, a pair of the objective lenses 46 and 47, and the half mirror 44 and the total reflection mirror 45 which guide luminous flux to a pair of the objective lenses 46 and 47 are provided, so that it becomes possible to support four kinds of discs with three wavelengths without the need of complicated structure as in the first embodiment.
Further, since the objective lens 46 corresponding to the BD was set for BD discs only and the objective lens 47 corresponding to HD-DVDs was constituted of a diffractive lens which can support three kinds of discs including HD-DVDs, DVDs and CDs, an optical system can be composed of low-cost objective lenses corresponding to the thickness of the cover layer of the discs.
Although the ratio of reflection to transmission of the half mirror 44 is set as 1 to 1 in the present embodiment, the present invention is not limited to this ratio. In the case where either the BD or the HD-DVD requires only the power for reproduction, or in the case where it is desired to give priority to the reproduction performance of either the BD or the HD-DVD, changing the ratio of the reflection to transmission in the half mirror 44 makes it possible to set a ratio of power allotted to the BD side to the power allotted to the HD-DVD side at, for example, 7 to 3.
In the above structure, in the case of recording information on and reproducing information from BD discs, as shown in
Moreover, in the case of recording information on and reproducing information from HD-DVD discs, as shown in
As mentioned above, according to the present embodiment, inexpensive plate components are used as the half mirror and the total reflection mirror. Therefore, it becomes possible to provide an inexpensive and stable optical pickup device.
Embodiments of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Number | Date | Country | Kind |
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2006-311639 | Nov 2006 | JP | national |