Optical pickup for recording and reproducing information with a plurality of types of optical information recording mediums

An optical pickup device in which a hologram element has a plurality of different diffraction directions. In the tracking standard state, the hologram element is divided into six areas by a straight line connecting two strength center points of two light beams, and by two straight lines that are perpendicular to the straight line. By adding the amount of light received by an area demarcated by two straight lines that pass the two strength center points, to the amount of light received by one of two outer areas sandwiching the area depending on the type of the light beam, it is possible to obtain a well-balanced tracking error signal for each of the two light beams.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2005/017119 filed on Sep. 16, 2005, which in turn claims the benefit of Japanese Application No. 2004-331789, filed on Nov. 16, 2004, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an optical pickup device for recording and reproducing information with a plurality of types of optical information recording mediums by outputting selectively two light beams of different wavelengths, and more specifically relates to a technology for obtaining high-accuracy tracking error signals in a stable manner from both light beams of the different wavelengths.

BACKGROUND ART

Currently, Compact Discs (CDs) have the largest market among various optical information recording mediums. CDs are recorded or reproduced with use of near-infrared semiconductor lasers whose wavelength is in a range of 780 nm to 820 nm. Digital Versatile Discs (DVDs) which have spread rapidly, are recorded or reproduced with use of red semiconductor lasers whose wavelength is even shorter and is in a range of 635 nm to 680 nm to make the light spot smaller.

From the market there is a demand for a drive device that can reproduce both the two types of optical information recording mediums conforming to different standards. Conventionally, a reproduction-dedicated optical pickup device, shown inFIG. 1, has been proposed (see, for example, Document 1). The operation principle of the conventional optical pickup device is as follows.

As shown inFIG. 1, an optical pickup device2includes light sources3and4, a hologram element7, a light receiving element substrate14, and a reflection mirror15, and reads information from an optical information recording medium1. The light source3conforms to the DVD standard, and emits a laser light beam having 650 nm of wavelength. The light source4conforms to the CD standard, and emits a laser light beam having 780 nm of wavelength.

The reflection mirror15guides laser light beams emitted from the light sources3and4to the optical information recording medium1. The hologram element7diffracts, by diffraction areas5and6thereof, laser light beams reflected from the optical information recording medium1. The light receiving element substrate14includes light receiving elements8-13, and receives light beams diffracted by the hologram element7.

A laser light beam emitted from the light source3enters the light receiving elements8-11. From output signals of the light receiving elements8-11, a focus error signal is detected by the Spot Size Detection (SSD) method, a tracking error signal is detected by the Differential Phase Detection (DPD) method, and a reproduction signal is detected.

The laser light beam emitted from the light source4enters the light receiving elements8,9,12, and13. From output signals of the light receiving elements8,9,12, and13, a focus error signal is detected by the Spot Size Detection method, a tracking error signal is detected by the 3-beam method or the Push-Pull (PP) method, and a reproduction signal is detected.

It should be noted here that a write once read many CD (CD-R) can also be reproduced using the light source3.

DISCLOSURE OF THE INVENTION

The Problems the Invention is Doing to Solve

However, according to the optical pickup device2, only the main light beam of one of the light beams emitted from the light sources3and4can pass through the center of the hologram element7. The other light beam, whose main light beam cannot pass through the center of the hologram element7causes an unbalance in the amount of light, between the light beams diffracted by the hologram element7, even if there is no tracking error.

In the push-pull method, a tracking error is detected from an unbalance in the amount of light between the light beams reflected from the optical information recording medium1. As a result, a very complicated process is required to detect a tracking error accurately when the push-pull method is adopted in the conventional technology. Also, in the differential phase detection method, a tracking error is detected from a phase difference between the diffracted light beams. Accordingly, it is difficult to detect a tracking error in a stable manner when the differential phase detection method is adopted in the conventional technology.

Furthermore, a tracking control by, for example, the Differential Push-Pull (DPP) method is required when information is recorded on an optical information recording medium. In the differential push-pull method, a tracking error is detected from an unbalance in the amount of light between the 0 order diffracted light beam and the ±1storder diffracted light beams output from the hologram element7. The optical pickup device2does not have a structure for performing the process by the differential push-pull method.

An object of the present invention is therefore to provide an optical pickup device for recording and reproducing information with a plurality of types of optical information recording mediums by outputting selectively two light beams of different wavelengths, where the optical pickup device can obtain high-accuracy tracking error signals in a stable manner from both light beams of the different wavelengths.

Means to Solve the Problems

The above-described object is fulfilled by an optical pickup device for recording and reproducing information on either of different optical information recording mediums, using light beams of different wavelengths according to types of the recording mediums, comprising: a semiconductor laser element operable to output selectively two light beams of different wavelengths; a hologram element operable to diffract light beams reflected from an optical information recording medium; six light receiving elements operable to receive light beams diffracted by the hologram element and perform a photoelectric conversion on the received light beams; and an output circuit operable to generate a tracking error signal from signals output from the light receiving elements, and output the generated tracking error signal, wherein the light beams reflected from the optical information recording mediums have strength centers thereof, respectively at two different points on the hologram element in correspondence with the different wavelengths, the hologram element is divided into six areas by a straight line connecting the two strength center points, and by two straight lines that are perpendicular to the straight line and respectively pass the two strength center points, and light beams diffracted by the six areas of the hologram element are respectively received by the six light receiving elements in a one-to-one correspondence with each other.

Effects of the Invention

With the above-stated structure, in the tracking standard state, four areas of the hologram element receive an equivalent amount of light reflected from the optical information recording mediums, for each of the optical information recording mediums, where the hologram element is divided into the four areas by the straight line connecting the two strength center points, and by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points in correspondence with a type of one of the optical information recording mediums that is currently reflecting a light beam.

Accordingly, in the tracking standard state, it is possible to generate a well-balanced, high-accuracy tracking error signal from signals each of which is obtained by adding together signals from light receiving elements, which have received light beams diffracted by a different one of the four areas of the hologram element.

As described above, due to the characteristic shape of the hologram element, the optical pickup device of the present invention can obtain well-balanced, high-accuracy tracking error signals in a stable manner, merely by adding signals from appropriate light receiving elements according to the type of one of the optical information recording mediums that is currently reflecting a light beam, to signals from an area of the hologram element sandwiched by the two straight lines that are perpendicular to the straight line connecting the two strength center points and respectively pass the two strength center points.

The above-stated optical pickup device may further comprise: a diffraction grating operable to diffract light beams into 0 order diffracted light beams, +1storder diffracted light beams, and −1storder diffracted light beams, on light paths from the semiconductor laser element to the optical information recording medium; and three tracking light receiving elements operable to receive diffracted light beams from the hologram element that are generated by the hologram element by diffracting ±1storder diffracted light beams reflected from the optical information recording medium, and perform a photoelectric conversion on the received diffracted light beams, wherein the ±1storder diffracted light beams are diffracted by three areas of the hologram element and then diffracted light beams output from the three areas enter the three light receiving elements in a one-to-one correspondence with each other, wherein the hologram element is divided into the three areas by the two straight lines that are perpendicular to the straight line connecting the two strength center points and pass the two strength center points, respectively.

In the above-stated optical pickup device, the diffraction grating may be divided into a central portion and outer portions by two straight lines that are substantially parallel to each other, the central portion has higher diffraction efficiency of the 0 order diffracted light beams than the outer portions, and gratings formed in the outer portions meet the two straight lines obliquely.

With the above-described structure, a tracking error signal can be obtained from the 0 order diffracted light beam and the ±1storder diffracted light beams, with respect to each type of light beam. This enables the tracking control to be performed by the differential push-pull method using the tracking error signal.

Especially, it is possible to increase the strength of each main beam by setting, for each main beam, the diffraction efficiency of the central portion of the diffraction grating to be larger than that of the outer portions. This increases the efficiency in recording and reproducing information.

In the above-stated optical pickup device, the output circuit may generate the tracking error signal from signals each of which is obtained by adding together signals from light receiving elements, which have received light beams diffracted by a different one of four areas of the hologram element, wherein the hologram element is divided into the four areas by the straight line connecting the two strength center points, and by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points in correspondence with a type of one of the optical information recording mediums that is currently reflecting a light beam.

In the above-stated optical pickup device, the output circuit may generate the tracking error signal from (i) a signal that is obtained by adding together signals from light receiving elements, which have received light beams diffracted by four areas of the hologram element, wherein the hologram element is divided into the four areas by the straight line connecting the two strength center points, and by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points depending on a type of one of the optical information recording mediums that is currently reflecting a light beam, and (ii) a signal that is obtained by adding together signals from tracking light receiving elements, which have received light beams diffracted by two areas of the hologram element, wherein the hologram element is divided into the two areas by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points depending on a type of one of the optical information recording mediums that is currently reflecting a light beam.

With the above-stated structure, appropriately added-up signals are obtained from the output circuit for each type of light beam, thus the addition needs not be performed by an external circuit.

The above-stated optical pickup device may further comprise focusing light receiving elements operable to receive −1storder diffracted lights from the hologram element that are generated by the hologram element by diffracting the 0 order diffracted light beams that are generated by the diffraction grating by diffracting the light beams, and to perform a photoelectric conversion on the received −1storder diffracted lights, wherein the output circuit generates a focus error signal from signals output from the focusing light receiving elements, and outputs the generated focus error signal.

In the above-stated optical pickup device, each of the six areas of the hologram element may be divided into two types of partial areas that have different diffraction angles, the two types of partial areas form beam spots that are symmetrical with respect to a light emission point of the semiconductor laser element, and the focusing light receiving elements receive light beams to form beam spots that are symmetrical with beam spots formed on the six light receiving elements with respect to the light emission point of the semiconductor laser element.

With the above-stated structure, it is possible to perform the focus control using, among the diffracted light beams obtained from the hologram element, diffracted light beams that are not used in the tracking control.

Especially, the symmetric property of the spot shape is increased by the structure in which the focusing light receiving elements receive images that are symmetrical with images received by the light receiving elements with respect to the light emission point of the semiconductor laser element. Accordingly, this reduces the detection error attributed to the asymmetry of the spot shape, when the spot side detection method is used.

The above-stated optical pickup device may further comprise a switch circuit that is used to add together: (i) for each of four areas of the hologram element, signals from light receiving elements which have received light beams diffracted by the four areas, wherein the hologram element is divided into the four areas by the straight line connecting the two strength center points, and by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points depending on a type of one of the optical information recording mediums that is currently reflecting a light beam, and (ii) for each of two areas of the hologram element, signals from tracking light receiving elements which have received light beams diffracted by the two areas, wherein the hologram element is divided into the two areas by one of the two straight lines that is perpendicular to the straight line and passes one of the two strength center points depending on a type of one of the optical information recording mediums that is currently reflecting a light beam.

With the above-described structure, the advantageous effects described above can be obtained.

In the above-stated optical pickup device, light receiving elements and tracking light receiving elements, which receive light beams diffracted by an area of the hologram element sandwiched by the two straight lines that are perpendicular to the straight line connecting the two strength center points and respectively pass the two strength center points, maybe separated into different portions in correspondence with types of the optical information recording mediums.

With the above-described structure, the light receiving elements, which receive light beams diffracted by the area of the hologram element sandwiched by the two straight lines that are perpendicular to the straight line connecting the two strength center points, are separated into different portions in correspondence with types of the optical information recording mediums. This makes it possible to obtain signals for each type of laser beam. When this happens, a switch circuit is not required to add signals for each type of the optical information recording mediums. As a result, the circuit structure can be simplified, and an appropriate tracking error signal can be obtained for each type of the optical information recording mediums.

The above-stated optical pickup device may further comprise a collimator lens operable to collimate light beams, wherein an optical axis of the collimator lens passes one of the strength centers which are held on the hologram element by the light beams reflected from the optical information recording medium.

With the above-described structure, the optical axis of the collimator lens matches the main light beam of one of the two light beams. This makes it possible to simplify, to some extent, the process of adjusting the optical axis of the present optical pickup device with the optical axis of the collimator lens.

In the above-stated optical pickup device, the light receiving elements and the semiconductor laser element may be provided on an integrated circuit substrate.

In the above-stated optical pickup device, the semiconductor laser element may be a monolithic 2-wavelength semiconductor laser element, and has been formed on the integrated circuit substrate by a semiconductor process.

With the above-described structures, the semiconductor laser element and the light receiving elements are provided on the same integrated circuit substrate. This makes it possible provide an optical pickup device, in which the semiconductor laser element and the light receiving elements are aligned with high accuracy, to the users.

Especially, by forming both the semiconductor laser element and the light receiving elements in the semiconductor process, it is possible to manage the alignment and the light beam emission interval of both with a high accuracy, namely, with the measurement accuracy of the semiconductor process.

In the above-stated optical pickup device, the integrated circuit substrate, the hologram element, and the diffraction grating may be loaded in one package.

With the above-described structures, it is possible provide an optical pickup device, in which even the hologram element and the diffraction grating are aligned with high accuracy, to the users. Also, providing a plurality of optical components in one package reduces the number of optical components that are to be managed by the user, thus contributes to the reduction of the assembly cost.

DESCRIPTION OF CHARACTERS

BEST MODE FOR CARRYING OUT THE INVENTION

An optical pickup device in Embodiment 1 of the present invention will be described with reference to the attached drawings.

(1) Entire Structure

FIGS. 2A and 2Bschematically show the entire structure of the optical pickup device in Embodiment 1 of the present invention.

As shown inFIGS. 2A and 2B, an optical pickup device100includes semiconductor lasers103and106, a diffraction grating107, a hologram element108, light receiving element groups109,110,111and112, an integrated circuit substrate113, a collimator lens114, and an objective lens115.

The semiconductor laser103emits a light beam102having a wavelength adapted to recording and reproducing data with an optical information recording medium101. The semiconductor laser106emits a light beam105having a wavelength adapted to recording and reproducing data with an optical information recording medium104. It should be noted here that the wavelength of the light beam102is shorter than that of the light beam105.

The diffraction grating107diffracts the light beams102and105into 0 order diffracted light (main beam), +1storder diffracted light (sub beam) and −1storder diffracted light (sub beam). The hologram element108diffracts the light beams102and105that were reflected on the optical information recording mediums101and104, respectively. The light receiving element groups109-112receive diffracted light that comes after diffraction by the hologram element108, and perform a photoelectric conversion on the received diffracted light.

An output circuit (not illustrated) is also loaded on the integrated circuit substrate113, as well as the semiconductor lasers103and106, diffraction grating107, hologram element108, and light receiving element groups109-112. The collimator lens114collimates the light beams102and105. The objective lens115concentrates the light beams102and105on the optical information recording mediums101and104, respectively.

The optical pickup device100also includes an optical information recording medium identifying unit that identifies the type of the optical information recording medium. The optical pickup device100determines which of the semiconductor lasers103and106to drive, based on the type of the optical information recording medium identified by the optical information recording medium identifying unit.

FIG. 2Ashows light paths of the light beams102and105from the semiconductor lasers103and106to the optical information recording mediums101and104, respectively.FIG. 2Bshows light paths of the light beams102and105from the optical information recording mediums101and104to the light receiving element groups109-112, respectively.

The X, Y and Z axes shown in the drawings respectively represent the radial direction, the tangential direction, and the direction perpendicular to the plane of the recording surface, of the optical information recording mediums101and104when the optical pickup device100is in use. It should be noted here that in the following description, the X, Y and Z axes refer to these directions, respectively.

FIG. 3is an outer perspective view showing the structure of the diffraction grating107. The diffraction grating107is a rectangular plate made of a translucent material, and is divided into a central portion501and outer portions502by two substantially parallel lines. The central portion501and the outer portions502differ from each other in diffraction efficiency.

To increase the efficiency in recording and reproducing information with the optical information recording mediums, it is necessary to increase the strength of the main beams. To increase the strength of the main beams, it is most preferable that the central portion501diffracts the light beams into 0 order diffracted lights with the diffraction efficiency of 100%. For example, the central portion501maybe formed as a non-grating area without the grating. With this structure, the central portion501does not generate the ±1storder diffracted lights, and the strength of the 0 order diffracted lights is maximized.

In the outer portions502, gratings have been formed to have such depths that enable the diffraction efficiency in diffracting the light beams102and105into the ±1storder diffracted lights102s1,102s2,105s1and105s2to be maximized. With this structure, it is possible to maximize the strength of the ±1storder diffracted lights generated by the outer portions502.

With such maximized strengths of the 0 order diffracted lights and ±1storder diffracted lights, the light use efficiency of the optical pickup device100is increased to the maximum.

It should be noted here that the grating of the outer portions502may be tilted by a predetermined degree of angle with respect to the central portion501.

FIG. 4is a plan view showing the structure of the hologram element108. In the standard state of the tracking, namely, in the state where there is no tracking error, the light beam102reflected on the optical information recording medium enters the area (encircled by a solid line in the drawing) where a point132on the hologram element108is the strength center, and the light beam105reflected on the optical information recording medium enters the area (encircled by a broken line in the drawing) where a point135is the strength center,.

The hologram element108is divided into six areas116-121by a straight line140connecting the points132and135, and by two straight lines142and145perpendicular to the straight line140. The areas116-121diffract the incident light into different directions, respectively.

With such a structure, the light beam102is divided equally into four areas by the straight lines140and142, and the light beam105is divided equally into four areas by the straight lines140and145.

That is to say, the light beam102is divided equally into an area116, an area117, an area being a combination of areas118and120, and an area being a combination of areas119and121. Also, the light beam105is divided equally into an area120, an area121, an area being a combination of areas116and118, and an area being a combination of areas117and119.

Each of the areas116-121is divided into positive areas and negative areas that are both rectangular and alternately arranged, by straight lines being parallel to straight lines142and145. In the positive and negative areas, gratings are provided such that the areas project images, which are symmetrical with respect to a point, onto a same position. The areas116-121are divided into positive areas116a-121aand negative areas116b-121b, respectively.

The optical members may be arranged in such a way that the main light beam of the light beam102emitted from the semiconductor laser103matches the optical axis of the collimator lens114. The widths of the areas18and119of the hologram element108in the X axis direction are determined based on the distance between the objective lens115and the collimator lens114.

(2) Beam Spots on Integrated Circuit Substrate113

FIG. 5is a plan view showing beam spots formed on the integrated circuit substrate113by the light beams102and105. InFIG. 5, the outline signs indicate the beam spots formed by the light beams102, and the black signs indicate the beam spots formed by the light beams105. Also, rectangular areas encircled by the broken lines indicate the positions of the light receiving element groups109-112.

The dot L1and L2indicate the light emission points of the semiconductor lasers103and106, respectively. In the case where a reflection mirror is provided on the integrated circuit substrate113to guide the light to the optical information recording mediums as shown inFIG. 1, the dots L1and L2indicate the reflection points on the reflection mirror.

(a) Beam Spots Formed by Light Beam102

The beam spots formed by the light beam102on the integrated circuit substrate113will be described.

FIG. 6Ais a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas116-121of the hologram element108after diffraction of the 0 order diffracted light102m, which is output from the diffraction grating107after diffraction of the light beam102.FIG. 6Bis a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas116-121of the hologram element108after diffraction of the ±1storder diffracted lights102s1and102s2, which are output from the diffraction grating107after diffraction of the light beam102.

InFIG. 5, the beam spots L101c, L106d, L101d, L106c, L102c, L105d, L102d, L105c, L103c, L104d, L103d, and L104care formed by the ±1storder diffracted lights output from the areas116-121of the hologram element108after diffraction of the 0 order diffracted light102m, which is output from the diffraction grating107after diffraction of the light beam102(FIG. 6A).

(b) Beam Spots Formed by Light Beam105

The beam spots formed by the light beam105on the integrated circuit substrate113will be described.

FIG. 7Ais a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas116-121of the hologram element108after diffraction of the 0 order diffracted light105m, which is output from the diffraction grating107after diffraction of the light beam105.FIG. 7Bis a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas116-121of the hologram element108after diffraction of the ±1storder diffracted lights105s1and105s2, which are output from the diffraction grating107after diffraction of the light beam105.

In this way, diffracted lights output from the same area of the hologram element108enter the integrated circuit substrate113at adjacent positions and form beam spots on the same light receiving element, regardless of whether the diffracted lights belong to the light beam102or105.

(3) Light Receiving Elements

The light receiving elements provided in the optical pickup device100will be described.

FIG. 8is a plan view showing an arrangement of the light receiving element groups109-112on the integrated circuit substrate113. The arrangement of the light receiving element groups109-112shown inFIG. 8matches the arrangement of the light receiving element groups109-112indicated by the broken line inFIG. 5.

As shown inFIG. 8, each of the light receiving element groups109-112is composed of a plurality of light receiving elements that align straight in the Y axis direction. Each of the light receiving element groups109-111is composed of four light receiving elements109a-109d,110a-110d, and111a-111d, respectively. The light receiving element group112is composed of five light receiving elements112a-112e.

The light receiving element groups109-111are used for detecting a tracking error signal. The light receiving element group112is used for detecting a focus error signal.

(4) Output Circuit

The output circuit provided on the integrated circuit substrate113will be described.

FIG. 9is a circuit diagram showing an equivalent circuit of the output circuit. As shown inFIG. 9, the output circuit includes 11 pieces of current/voltage amplification conversion circuits (hereinafter merely referred to as “amplification circuits”)601-611.

The amplification circuits601-606convert and amplify the current signals output from the light receiving elements109b,110b,111b,109c,110c, and111c, and output signals T1, T3, T5, T2, T4, and T6, respectively.

The amplification circuits607-610convert and amplify the sum of light receiving elements109aand109d, the sum of light receiving elements110aand110d, the sum of light receiving elements111aand111d, and the sum of light receiving elements111band111d, and output signals T7-T9and F1, respectively.

The amplification circuit611converts and amplifies the sum of light receiving elements111a,111cand111e, and outputs signal F2.

In this way, it is possible to reduce the adverse effect of the noise by converting current signals, which are output from the light receiving elements, to voltage signals. This improves the recording/reproduction speed.

(5) Detection of Focus and Tracking Error Signals

A method of detecting the focus error signal and the tracking error signal will be described.

(a) Detection of Focus Error Signals

The optical pickup device100detects focus error signals FE from the signals F1and F2by the spot size detection method, with respect to each of the light beams102and105. That is to say,
FE1=F1−F2   (Equation 1).
(b) Detection of Tracking Error Signals by Phase Difference Detection Method

The optical pickup device100detects tracking error signals TE(DVD) and TE(CD) with respect to the light beams102and105, by the phase difference detection method. That is to say,

TE⁡(DVD)=(phase⁢⁢difference⁢⁢between⁢⁢T⁢⁢1⁢⁢and⁡(T⁢⁢3+T⁢⁢5))+⁢(phase⁢⁢difference⁢⁢between⁢⁢T⁢⁢2⁢⁢and⁢(T⁢⁢4+T⁢⁢6),(Equation⁢⁢2)TE⁡(CD)=(phase⁢⁢difference⁢⁢between(T⁢⁢1+T⁢⁢3)⁢⁢and⁢⁢T⁢⁢5)+(phase⁢⁢difference⁢⁢between(T⁢⁢2+T⁢⁢4)+T⁢⁢6).(Equation⁢⁢3)
(c) Detection of Tracking Error Signals by Differential Push-Pull Method

The optical pickup device100detects tracking error signals TE(DVD) and TE(CD) with respect to the light beams102and105, by the differential push-pull method. That is to say,

TE⁡(DVD)=(T⁢⁢1+T⁢⁢2)-(T⁢⁢3+T⁢⁢4+T⁢⁢5+T⁢⁢6)-k⁡[T⁢⁢7-(T⁢⁢8+T⁢⁢9)],(Equation⁢⁢4)TE⁡(CD)=(T⁢⁢1+T⁢⁢2+T⁢⁢3+T⁢⁢4)-(T⁢⁢5+T⁢⁢6)-k⁡[(T⁢⁢7+T⁢⁢8)-T⁢⁢9].(Equation⁢⁢5)
Here, “k” is a constant with which each of the tracking error signals TE (DVD) and TE (CD) represents 0 when there is no tracking error.

It is understood from Equations 2 through 6 that it is possible to detect tracking error signals for DVD by adding signals T3, T4and T8to signals T5, T6and T9, respectively, regardless of whether the phase difference detection method or the differential push-pull method is used. Also, it is possible to detect tracking error signals for CD by adding signals T3, T4and T8to signals T1, T2and T7, respectively, regardless of whether the phase difference detection method or the differential push-pull method is used.

(6) Modification of Output Circuit

Next, a modification of the output circuit in the present embodiment will be described.

FIG. 10is a circuit diagram showing an equivalent circuit of the output circuit in the present modification. As shown inFIG. 10, the output circuit of the modification differs from the output circuit of the embodiment shown inFIG. 9in that it additionally includes switch circuits701-703.

The switch circuit701makes a connection such that an output from an amplification circuit602(corresponding to T3inFIG. 9) is added to an output from an amplification circuit603(corresponding to T5), when a recording or reproduction is performed with DVD. Also, the switch circuit701makes a connection such that an output from the amplification circuit602is added to an output from an amplification circuit601(corresponding to T1), when a recording or reproduction is performed with CD. That is to say, a signal representing a sum of T5and T3is output as T5a.

The switch circuit702makes a connection such that an output from an amplification circuit605(corresponding to T4) is added to an output from an amplification circuit606(corresponding to T6), when a recording or reproduction is performed with DVD. That is to say, a signal representing a sum of T4and T6is output as T6a. Also, the switch circuit702makes a connection such that an output from the amplification circuit605is added to an output from an amplification circuit604(corresponding to T2), when a recording or reproduction is performed with CD. That is to say, a signal representing a sum of T2and T4is output as T2a.

The switch circuit703makes a connection such that an output from an amplification circuit608(corresponding to T8) is added to an output from an amplification circuit609(corresponding to T9), when a recording or reproduction is performed with DVD. That is to say, a signal representing a sum of T8and T9is output as T9a. Also, the switch circuit703makes a connection such that an output from the amplification circuit608is added to an output from an amplification circuit607(corresponding to T7), when a recording or reproduction is performed with CD. That is to say, a signal representing a sum of T7and T8is output as T7a.

With use of the switch circuits701-703that function as described above, it is possible to obtain a tracking error signal TE(DPD) by the phase difference detection method, for both DVD and CD, from the following equation.

Also, it is possible to obtain a tracking error signal TE(DPP) by the differential push-pull method, for both DVD and CD, from the following equation.

TE⁡(DPP)=(T⁢⁢1⁢a+T⁢⁢2⁢a)-(T⁢⁢5⁢a+T⁢⁢6⁢a)-k⁡(T⁢⁢7⁢a+T⁢⁢9⁢a).(Equation⁢⁢10)
Here, “k” is a constant with which TE(DPP) is 0 when the tracking is in the normal state.

With the above-stated structure, the output circuit of the modification outputs a smaller number of signals than the output circuit shown inFIG. 9, and an external circuit for the addition calculation is not required.

As described above, according to the present embodiment, it is possible to detect a focus/tracking error signal for achieving the recording and reproduction in a stable manner, for both the two types of optical information recording mediums, DVD and CD.

Also, it is possible to completely separate the signal circuit for detecting a focus error signal and the signal circuit for detecting a tracking error signal, and DVD and CD can share the signal circuits for detecting focus and tracking error signals. This makes it possible to simplify the signal processing circuit.

Embodiment 2 of the present invention will be described. The optical pickup device in Embodiment 2 has almost the same structure as the optical pickup device in Embodiment 1, except for the structure of the light receiving element. The following description will center of the differences.

(1) Entire Structure

FIGS. 11A and 11Bschematically show the entire structure of the optical pickup device in Embodiment 2.

FIG. 11Ashows light paths of light beams202and205from semiconductor lasers203and206to optical information recording mediums201and204, respectively.FIG. 11Bshows light paths of light beams202and205from optical information recording mediums201and204to light receiving element groups209-215, respectively. The X, Y and Z axes are the same as those shown inFIGS. 2A and 2B.

As shown inFIGS. 11A and 11B, an optical pickup device200includes semiconductor lasers203and206, a diffraction grating207, a hologram element208, light receiving element groups209-215, an integrated circuit substrate216, a collimator lens217, and an objective lens218.

The semiconductor lasers203and206emit light beams202and205having wavelengths conforming to the standards of the optical information recording mediums201and204, respectively. It should be noted here that the wavelength of the light beam202is shorter than that of the light beam205.

The optical pickup device200also includes an optical information recording medium identifying unit that identifies the type of the optical information recording medium that is an object of recording/reproduction. The optical pickup device200determines which of the semiconductor lasers203and206to drive, based on the type of the optical information recording medium identified by the optical information recording medium identifying unit.

The diffraction grating207diffracts the light beams202and205into 0 order diffracted light (main beam), +1storder diffracted light (sub beam, not illustrated) and −1storder diffracted light (sub beam, not illustrated), on the light paths from the semiconductor lasers203and206to the hologram element208, respectively. The structure of the diffraction grating207is the same as the structure of the diffraction grating107in Embodiment 1 (seeFIG. 3).

The hologram element208diffracts the light beams202and205that were reflected on the optical information recording mediums201and204, respectively. The light receiving element groups209-215receive diffracted light that comes after diffraction by the hologram element208, and performs a photoelectric conversion on the received diffracted light. The signals, which are generated by the photoelectric conversion performed by the light receiving element groups209-215, are output via an output circuit that is not illustrated.

The semiconductor lasers203and206, light receiving element groups209-215, and output circuit are loaded on the integrated circuit substrate216.

A collimator lens217and an objective lens218are provided on the light paths from the hologram element208to the optical information recording mediums201and204. It is preferable that the optical members are arranged in such a way that the main light beam of the light beam202emitted from the semiconductor laser203matches the center of the optical axis of the collimator lens217.

(3) Structure of Hologram Element208

Next, the structure of the hologram element208will be described.FIG. 12is a plan view showing the structure of the hologram element208.

InFIG. 12, points232and235represent strength centers of the light beam202and205reflected on the optical information recording mediums201and204, respectively, in the standard state of the tracking, namely, for example, in the state where there is no tracking error.

The main surface of the hologram element208is divided into six areas219-224by a straight line208connecting the points232and235, and by two straight lines241and242that are perpendicular to the straight line208at the points232and235. The areas219-224diffract the light beams202and205into different directions, respectively.

In the above-described structure where the main surface of the hologram element208is divided into the six areas, four areas, which are area219, area220, a combination of areas221and223, and a combination of areas222and224, receive an equivalent amount of light from a reflected light of the light beam202after reflection on the optical information recording medium201in the standard state of the tracking.

Similarly, the four areas, which are area219, area220, a combination of areas221and223, and a combination of areas222and224, receive an equivalent amount of light from a reflected light of the light beam205after reflection on the optical information recording medium204.

Each of the areas219-224is divided into positive areas and negative areas that are both rectangular and alternately arranged. Namely, the areas219-224are divided into positive areas219a-224aand negative areas219b-224b, respectively. In the positive and negative areas, gratings are provided such that images that are symmetrical with respect to a point are focused onto a same light receiving element.

The light paths of the light beams202and205change depending on the distance between the collimator lens217and the objective lens218, and the positions of the points232and235change depending on the positional relationship among the collimator lens217, the objective lens218, and the hologram element208. Accordingly, how the main surface of the hologram element208is divided into areas is determined based on these positional relationships.

(3) Beam Spots on Integrated Circuit Substrate216

FIG. 13is a plan view showing beam spots (hereinafter merely referred to as spots) formed on the integrated circuit substrate216by the light beams202and205. InFIG. 13, the outline signs indicate the spots formed by the light beams202, and the black signs indicate the spots formed by the light beams205. Also, rectangular areas encircled by the broken lines indicate the positions of the light receiving element groups209-215.

The dots L1and L2indicate the light emission points of the semiconductor lasers203and206, respectively. In the case where a reflection mirror is provided on the integrated circuit substrate216to guide the light to the optical information recording mediums as shown inFIG. 1, the dots L1and L2indicate the reflection points on the reflection mirror.

(a) Beam Spots Formed by Light Beam202

The beam spots formed by the light beam202on the integrated circuit substrate216will be described.

FIG. 14Ais a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the 0 order diffracted light202m, which is output from the diffraction grating207after diffraction of the light beam202.FIG. 14Bis a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the ±1storder diffracted lights202s1and202s2, which are output from the diffraction grating207after diffraction of the light beam202.

InFIG. 13, the beam spots L1101c, L1106d, L1101d, L1106c, L1102c, L1105d, L1102d, L1105c, L1103c, L1104d, L1103d, and L1104care formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the 0 order diffracted light202m, which is output from the diffraction grating207after diffraction of the light beam202(FIG. 14A).

(b) Beam Spots Formed by Light Beam205

The beam spots formed by the light beam205on the integrated circuit substrate216will be described.

FIG. 15Ais a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the 0 order diffracted light205m, which is output from the diffraction grating207after diffraction of the light beam205.FIG. 15Bis a table indicating the spots that are formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the ±1storder diffracted lights205s1and205s2, which are output from the diffraction grating207after diffraction of the light beam205.

InFIG. 13, the beam spots L1201c, L1206d, L1201d, L1206c, L1202c, L1205d, L1202d, L1205c, L1203c, L1204d, L1203d, and L1204dare formed by the ±1storder diffracted lights output from the areas219-224of the hologram element208after diffraction of the 0 order diffracted light205m, which is output from the diffraction grating207after diffraction of the light beam205(FIG. 15A).

In this way, the areas219,220,222, and223diffract light so that the spots of the light beams202and205enter the same light receiving element. Also, the areas220and221diffract light so that the spots of the light beams202and205enter the different light receiving elements.

Next, the light receiving element groups209-215will be described.

FIG. 16is a plan view showing an arrangement of the light receiving element groups209-215on the integrated circuit substrate216.

As shown inFIG. 16, each of the light receiving element groups209-215is composed of a plurality of light receiving elements that align straight in the Y axis direction. Each of the light receiving element groups209,210,212, and214is composed of four tight receiving elements209a-209d,210a-210d,212a-212d, and211a-212d, respectively. Each of the light receiving element groups211,213, and215is composed of five light receiving elements211a-211e,213a-213e, and215a-215e, respectively.

The light receiving element group212receives a diffracted light from the areas220. and221of the hologram element208after diffraction of the light beam202, and outputs a signal that varies depending on the amount of the received light. The light receiving element group214receives a diffracted light from the areas220and221of the hologram element208after diffraction of the light beam205, and outputs a signal that varies depending on the amount of the received light.

In Embodiment 1, the light receiving element group110receives the ±1storder diffracted lights output from the areas118and119of the hologram element108after diffraction of the 0 order diffracted light102m, which is output from the diffraction grating107after diffraction of the light beam102, and the −1storder diffracted lights are not used.

On the other hand, in the present embodiment, the light receiving element group212receives the −1storder diffracted lights output from the areas211and212of the hologram element208after diffraction of the 0 order diffracted light202m, which is output from the diffraction grating207after diffraction of the light beam202, and the +1storder diffracted lights are not used.

(5) Output Circuit

FIG. 17is a circuit diagram showing an equivalent circuit of the output circuit provided on the integrated circuit substrate216.

As shown inFIG. 17, the amplification circuit701converts and amplifies the current signals output from the light receiving elements209band214c, and outputs a signal T11. The amplification circuit702converts and amplifies the current signals output from the light receiving elements209cand214b, and outputs a signal T12. The amplification circuit703converts and amplifies the current signals output from the light receiving elements210band212c, and outputs a signal T13. The amplification circuit704converts and amplifies the current signals output from the light receiving elements210cand212b, and outputs a signal T14.

The amplification circuit705converts and amplifies the current signals output from the light receiving elements209a,209d,214a, and214d, and outputs a signal T15. The amplification circuit706converts and amplifies the current signals output from the light receiving elements210a,210d,212a, and212d, and outputs a signal T16. The amplification circuit707converts and amplifies the current signals output from the light receiving elements211a,211d,213b,213d,215b, and215d, and outputs a signal F11.

The amplification circuit708converts and amplifies the current signals output from the light receiving elements211a,211c,211e,213a,213c,213e,215a,215c, and215e, and outputs a signal F12.

The signals output from the amplification circuit701-708are voltage signals. Since the voltage signals have higher tolerance for noise than the current signals, this structure improves the recording/reproduction speed.

(6) Detection of Focus and Tracking Error Signals

A method of detecting the focus error signal and the tracking error signal will be described, with respect to the light beams202and205.

(a) Detection of Focus Error Signals

The optical pickup device200detects focus error signals FE from the signals F11and F12by the spot size detection method, with respect to each of the light beams202and205. That is to say,
FE1=F11−F12   (Equation 11).
(b) Detection of Tracking Error Signals by Phase Difference Detection Method

The optical pickup device200detects a tracking error signal TE from the signals T11-T14by the phase difference detection method, with respect to each of the light beams202and205. That is to say,

TE=(phase⁢⁢difference⁢⁢between⁢⁢T⁢⁢11⁢⁢and⁢⁢T⁢⁢13)+(phase⁢⁢difference⁢⁢between⁢⁢T⁢⁢12⁢⁢and⁢⁢T⁢⁢14).(Equation⁢⁢12)
(c) Detection of Tracking Error Signals by Differential Push-Pull Method

The optical pickup device200detects tracking error signals TE from the signals T11-T16by the differential push-pull method, with respect to each of the light beams202and205. That is to say,

TE=(T⁢⁢11+T⁢⁢12)-(T⁢⁢13+T⁢⁢14)-k⁡(T⁢⁢15-T⁢⁢16),(Equation⁢⁢13)
Here, “k” is a constant with which the tracking error signal TE represents 0 when there is no tracking error.
(7) Conclusion

As described above, according to the present embodiment, it is possible to perform the recording and reproduction with accuracy with both the optical information recording mediums201and204which conform to different standards, since the semiconductor lasers203and206of the present embodiment emit the light beams202and205that have different wavelengths. Also, as is the case with Embodiment 1, it is possible to detect a focus/tracking error signal for in a stable manner.

Further, the structure of the present embodiment makes it possible to completely separate the signal system for detecting a focus error signal and the signal system for detecting a tracking error signal. The present embodiment differs from Embodiment 1 in that it enables the signal processing system to be simplified since it does not require a switch circuit for performing a selective addition.

Up to now, embodiments of the present invention have been described. However, not limited to these embodiments, the present invention can be modified variously, for example, as follows.

(1) In the above-described embodiments, single-wavelength semiconductor lasers are provided according to different types of optical information recording mediums, respectively. However, not limited to this, monolithic 2-wavelength semiconductor lasers may be provided instead.

FIG. 18is a cross-sectional view showing an entire structure of an optical pickup device in the present modification. As shown inFIG. 18, an optical pickup device300of the present modification is provided with a monolithic 2-wavelength semiconductor laser321, instead of the semiconductor laser104or106.

The accuracy of the light beam emission interval depends on the assembly accuracy in the case of the semiconductor lasers103and106, and depends on the diffusion accuracy in the case of the monolithic 2-wavelength semiconductor laser321. The present modification therefore improves the accuracy of the light beam emission interval. The same advantageous effect can also be obtained in Embodiment 2 by using the monolithic 2-wavelength semiconductor lasers instead of the semiconductor lasers203and206.

It should be noted here that the advantageous effects produced by the above-described embodiments do not change if this structure of the modification is adopted.

(2) In the above-described embodiments, the semiconductor lasers and the light receiving elements are provided on the integrated circuit substrate. However, the components such as the integrated circuit substrate may be loaded in one package.

FIG. 19is a cross-sectional view showing schematically the main structure of the optical pickup device in the present modification. As shown inFIG. 19, an optical pickup device400includes semiconductor lasers403and406, light receiving element groups409-412, an integrated circuit substrate413, a collimator lens414, an objective lens415, a single plate421, and a package422.

The semiconductor lasers403and406and the light receiving element groups409-412are provided on the integrated circuit substrate413. A diffraction grating407is provided within a surface of the single plate421that is opposed to the semiconductor lasers403and406. A hologram element408is provided within a surface of the single plate421that is opposed to the collimator lens414.

The package422has a flat bottom portion and a support portion that supports the single plate421. The package422and the single plate421are fixed in the state where the integrated circuit substrate413is disposed on the bottom portion of the package422, and the single plate421is supported by the support portion of the package422.

With this structure, in which the semiconductor lasers and the light receiving elements are provided in one package, it is possible to reduce the size of the optical pickup device, and consequently, it is possible to reduce the size of the recording/reproduction device in which the optical pickup device is loaded. Also, it is possible to reduce the number of components that are controlled in terms of the assembly accuracy of the recording/reproduction device. Accordingly, this structure of the modification improves the assembly accuracy and reduces the cost by simplifying the recording/reproduction device.

It should be noted here that the advantageous effects produced by the above-described embodiments do not change if this structure of the modification is adopted.

(3) Although not mentioned in the above-described embodiments, the term “DVD” used in this document refers to any of DVD, DVD-ROM, DVD-RAM, DVD-R, and DVD-RW, and the term “CD” used in this document refers to any of CD, CD-ROM, CD-R, and CD-RW.

INDUSTRIAL APPLICABILITY

The optical pickup device of the present invention can be used in an optical information processing device that records, reproduces, and deletes information to/from optical information recording mediums.