KR100189918B1 - Changeable photo pick up apparatus - Google Patents

Abstract

Disclosed is a disk compatible optical pickup apparatus having a different format.

The disclosed apparatus comprises: a light source for generating and irradiating light; A first optical path changing means for changing the traveling path of the incident light; An objective lens disposed on an optical path between the first optical path changing means and the recording medium for converging the incident light so that a light spot is formed on the recording medium; Light control means for adjusting the size of the light spot converged on the objective lens and formed on the recording medium; And a photodetector for receiving the light passing through the objective lens and the first light path changing means to detect an error signal and an information signal, wherein the first light source emits light of a predetermined wavelength to the light source, And second light path changing means for changing the path of the incident light so that the light emitted from the first light source and the light emitted from the second light source are directed to the recording medium, .

Description

Compatible optical pickup device

FIG. 1 is a schematic view showing an optical arrangement of a compatible optical pickup device according to a conventional example; FIG.

FIG. 2 is a schematic view showing an optical arrangement of a compatible optical pickup device according to another conventional mode.

FIG. 3 is a graph showing the sensitivity according to the wavelength of the light source when the CD-R is employed as the recording medium.

FIG. 4 is a schematic view for explaining a conventional disc player designed to overcome data destruction of a CD-R according to a conventional wavelength; FIG.

FIG. 5 is a schematic view showing the optical arrangement of a compatible optical pickup device according to the present invention; FIG.

FIG. 6 is a schematic view for explaining another embodiment of the light control means of FIG. 5; FIG.

Figs. 7 and 8 are schematic views for explaining a third embodiment of the light control means of Fig. 5; Fig.

Figures 9 and 10 are schematic diagrams for illustrating a fourth embodiment of the light control means of Figure 5;

DESCRIPTION OF THE REFERENCE NUMERALS

10: recording medium 110: first light source

112: second light source 116: second optical path changing means

118: Grating 120: First light path changing means

122: wavelength plate 124: collimating lens

126: objective lens 128: astigmatic lens

130: photodetector 140: light control means

141: hologram element 143: variable aperture

145: transparent member

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to an optical pickup apparatus, and more particularly, to a disc-compatible optical pickup apparatus compatible with disc-shaped recording media of different formats.

2. Description of the Related Art In general, an optical pickup device is used in a compact disc player (CDP), a digital video disc player (DVDP), a CD-ROM driver, a DVD-ROM driver or the like and performs recording / reproduction of information on a recording medium in a noncontact manner.

DVDP and DVD-ROM are high-density recording / playback devices that have been attracting attention in the field of video / audio. The optical pickup device employed in this DVDP adopts a CD family such as compact disc (CD), CD-R (recordable), CD-I and CD-G as well as a digital video disc The information recording and / or reproducing should be possible.

However, the thickness of the DVD has been standardized to be different from the thickness of the CD family due to the mechanical disc tilt tolerance and the numerical aperture of the objective lens. That is, the thickness of the existing CD family is 1.2 mm whereas the DVD is 0.6 mm. As described above, when the optical pickup device for DVD is applied to the CD family because the thicknesses of the CD family and the DVD are different from each other, spherical aberration due to the thickness difference is generated. This spherical aberration causes a problem that a sufficient light intensity necessary for recording an information signal is not obtained or a signal at the time of reproduction deteriorates.

Also, in terms of the wavelength of the reproduction light source, DVD was standardized as a wavelength region different from the CD family. That is, the wavelength of the reproduction light source for the existing CD family is approximately 780 nm, whereas the wavelength of the reproduction light source of the DVD is approximately 650 nm.

Due to such a difference in standardization, it is impossible to reproduce information recorded on a DVD with a normal CDP.

Therefore, in order to overcome the above-mentioned points, a disk compatible optical pickup apparatus having different formats as shown in FIGS. 1 and 2 has been disclosed.

FIG. 1 is an optical configuration diagram showing an embodiment of a disc compatible optical pick-up apparatus of a different format from the conventional one.

The objective lens 19, the beam splitter 15, the hologram element 17, and the photodetector 23 in its constitution. The light source 11 generates and emits light of a predetermined wavelength, for example, a wavelength of approximately 650 nm. The objective lens 19 converges the incident light so that a light spot is formed on the recording surface of the optical disc 10. The beam splitter 15 is located on the optical path between the light source 11 and the lens lens 19 to prevent the light reflected from the optical disk 10 from re-entering the light source 11. That is, most of the light 1 incident on the light source 11 passes straight through the beam splitter 15, and the light incident on the objective lens 19 is reflected to the photodetector 23 . The hologram element 17 is located on the optical path between the objective lens 19 and the beam splitter 15. The hologram element 17 separates the incident light into a zero-order light beam 3 and a + first-order light beam 5 and emits the separated light. The zero-order light (3) is substantially straight with respect to the incident light, and the + first-order light (5) diverges. Therefore, the zero-order light (3) and the + first-order light (5) form foci at different positions. The zero-order light beam 3 is used for a thin disc, that is, for the DVD 10a, and the + first-order light beam 5 is used for a relatively thick disc, that is, the CD 10b. The photodetector 23 receives the light reflected from the recording surface of the optical disc 10 and detects an RF information signal, a track error signal and a focus error signal.

The optical pickup apparatus further includes a grating (25) and a collimating lens (13). The grating 25 is positioned between the light source 11 and the beam splitter to diffract the incident beam into a 0-order diffraction beam, a ± 1-order diffraction beam and the like. The collimating lens 13 is disposed between the beam splitter 15 and the hologram element 17 to convert incident light into parallel light. Further, an astigmatic lens 21 is provided between the beam splitter 15 and the photodetector 23. When the distance between the objective lens 19 and the optical disk 10 is the ON focus, the circular light is converged on the photodetector 23 And if not, elliptical light is caused to converge on the photodetector 23.

This optical pickup apparatus separates the light emitted from the light source 11 into the 0-order light 3 and the +1-order light 5 in the hologram element 17. The separated light beams 3 and 5 are converged on the optical disc 10 while passing through the objective lens 19. When the DVD 10b is adopted as the optical disc 10, the information is recorded / reproduced by using the zero-order light beam 3. When the CD 10a is employed, the information is recorded by using the + / Playback.

FIG. 2 is an optical configuration diagram showing another embodiment of a disc compatible optical pick-up apparatus of a conventional format.

This disc compatible optical pick-up apparatus is substantially as described with reference to FIG. 1, and is characterized in that the hologram element (FIG. 17) is replaced by a variable stop 18. The variable diaphragm 18 is provided on the optical path between the objective lens 19 and the beam splitter 15 and appropriately adjusts the passage area, that is, the numerical aperture of the light incident from the light source 11 side. The opening diameter of the variable diaphragm 18 is adjusted to correspond to the thickness of the adopted disc. That is, the light in the central region is always passed, while the light in the peripheral region is selectively passed or blocked depending on the thickness of the employed disc. Since the size of the light spot can be adjusted by adjusting the diameter of the aperture of the variable diaphragm 18, it is possible to adopt a disc having a different thickness, for example, compatible with a DVD and a CD family.

The unexplained members are the same as or similar to the members having the same reference numerals described in FIG.

The present applicant has proposed a compatible optical pick-up apparatus in Korean Patent Application No. 95-31679 (an objective lens apparatus and a method of obtaining a stable focus servo signal and an optical pick-up apparatus using the method, a method of discriminating a disc having a different thickness, A method for reproducing and recording information from a disc, and a method for producing a lens) and 96-13918 (an optical pickup apparatus employing the objective lens apparatus and the objective lens apparatus).

The proposed optical pickup device is constructed so as to block or shield light in the intermediate region between the paraxial area around the optical axis of the objective lens, i.e., the paraxial area in which the spherical aberration hardly occurs, and the paraxial area, So that the interference of light of the light spot is suppressed.

The light having passed through the far axis region of the objective lens is applied to a relatively thin disc, for example, DVD, and the light passing through the near-axis region is applied to all discs, for example, a CD family and a DVD.

As described above, disc-compatible optical pick-up apparatuses of different formats use a single light source with a focus on overcoming the problems caused by disc-to-disc thickness differences. That is, the compatible optical pickup device employs a light source that emits light of a short wavelength (approximately 650 nm) conforming to the DVD format. In this case, deterioration of about 5% is generated as compared with the optical pickup device employing the light source that emits light in the wavelength region of 780 nm, but this is not a big problem because it is within the tolerance range during reproduction.

However, when a recordable CD-R, which is one of the CD family, is adopted as a recording medium, when using a light source that emits light in a wavelength region of approximately 650 nm, as shown in FIG. 3, Differs from the case of using a light source that emits light in a wavelength region. Since a conventional CD-R has an organic dye film recording layer as is widely known, when light in a 650 nm wavelength region is used due to a difference in sensitivity, a serious problem that data recorded in the CD-R is destroyed is caused.

To solve this problem, a new type of CD-R recording medium is being developed. Such a solution is not a fundamental solution for protecting data already recorded on a CD-R that has become widely available.

In order to overcome such a problem, as shown in FIG. 4, there has been proposed a method of employing both an optical pickup for DVD and an optical pickup for CD family in a compatible disc player.

This compatible disc player includes a spindle motor 30 on which a disc 10 is mounted and first and second guide rails 31 and 31 which are provided in the periphery of the spindle motor 30 in the radial direction of the disc 10 A first optical pickup device 32 mounted on the first guide rail 31 and performing a recording / reproducing function when a DVD is used as a disc, and a second optical pickup device 32 mounted on the second guide rail 33, And a second optical pickup device 34 installed to be slidable in the radial direction of the disc 10 and performing a recording / reproducing function when the disc 10 adopts a CD family.

The first optical pickup device 32 emits a light having a wavelength suitable for DVD, that is, a light having a wavelength of about 650 nm, and the second optical pickup device 34 is a light source, And emits light of a wavelength.

As described above, in the case where the compatible optical disk player is provided with two optical pick-up devices, it is possible to overcome the above-described problems, but it has a problem that the assemblability is poor, the miniaturization of the product is difficult, and the cost is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a compatible optical pickup apparatus which can adopt a disc having a different format and which has a simple structure.

According to an aspect of the present invention, there is provided an optical recording medium including a light source for generating and irradiating light, a first optical path changing means for changing the path of the incident light, A light control means for converging the incident light so as to form a light spot on the recording medium so as to form a light spot, a light control means for controlling the size of a light spot converged on the objective lens and formed on the recording medium, And a photodetector for detecting an error signal and an information signal by receiving light passing through the optical path changing means, the optical pickup device comprising: a first light source for emitting light of a predetermined wavelength to the light source; And a second light source for emitting light having a wavelength different from that of the light source, wherein the first light source and the second light source disposed at different positions convert the traveling path of the incident light so that the light emitted from the second light source is directed to the recording medium And a second optical path changing means is further included.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a configuration diagram showing the optical arrangement of the compatible optical pickup device according to the present invention.

As shown in the figure, the compatible optical pickup device includes a first light source 110 and a second light source 112 for generating and irradiating light, respectively, and a second light source 112 disposed at a predetermined position on the optical path, An objective lens 126 for converging incident light such that a light spot is formed on the recording medium 10, and a second optical path changing means 120 for converting the recording medium 10 A light control unit 140 for adjusting the size of a light spot formed on the objective lens 126 and the first optical path changing unit 120; And a photodetector 130 for detecting light.

The first light source 110 is a semiconductor laser that emits light of a wavelength suitable for the recording medium 10 of the new format, for example, the DVD 10b. That is, the wavelength of the light emitted from the first light source 110 is preferably 650 nm ± 20 nm.

The second light source 112 is a semiconductor laser that emits light of a wavelength suitable for a CD family 10a such as a CD, a CD-R, a CD-G and a CD-I, The wavelength of the light emitted from the second light source 112 is preferably 780 nm ± 20 nm.

Here, the first light source 110 and the second light source 112 are selectively driven. This drive mechanism may be switched by the user through a switch or the like, and a device for determining the thickness of the disk may be provided in the apparatus to automatically select the drive light source. Since the driving mechanism is based on well-known conventional means, detailed description thereof will be omitted.

The second optical path changing means 116 allows the light emitted from the first light source 110 and the second light source 112 to pass straight through and reflect the other light, 116 are arranged on the optical path so as to be directed to the first optical path changing means 120. [ It is preferable that the second light path changing means 116 is provided with a beam splitter which splits incident light at a predetermined light amount ratio and partially transmits the light and reflects the remaining light.

As shown in the figure, the beam splitter has a first incident surface 116a and a second incident surface 116b. The first incident surface 116a faces the first light source 110, And the surface 116b faces the second light source 112. [ Accordingly, the light emitted from the first light source 110 and incident on the first incident surface 116a is transmitted and reflected at a predetermined ratio at the interface 116d of the beam splitter.

Here, the reflected light is ignored, and the light transmitted to the emission surface 116c is used as effective light. On the other hand, light emitted from the second light source 112 and incident on the second incident surface 116b is transmitted through the interface 116d at a predetermined ratio, and the reflected light is used as effective light.

A polarization beam splitter that transmits light of a predetermined polarization among the incident light to the second optical path changing means 116 and reflects the remaining polarized light may be employed. This is because the first light source 110 and the second light source 112 can be manufactured so that light of P or S polarized light is emitted from the first light source 110 and the second light source 112, respectively. In the case where the polarization beam splitter is employed as the second optical path changing means 116, since the loss of light emitted from each of the two light sources 110 and 112 is small as compared with the case where the beam splitter is used, .

The first optical path changing means 120 guides the light emitted from the first light source 110 and the second light source 112 to the recording medium 10 and reflects the light reflected from the recording medium 10 Guided to the photodetector 130 without being re-incident to the two light sources 110 and 112. The first optical path changing means 120 may adopt a conventional beam splitter or a polarizing beam splitter which transmits only a predetermined polarized light. When the polarized beam splitter is used as the first optical path changing means 120, when the light incident on and passed through the two light sources 110 and 112 is reflected by the recording medium 10 and is incident again, A wave plate 122 for converting the polarization direction so as not to be re-incident on the two light sources 110 and 112 is further provided on the optical path between the polarization beam splitter 120 and the recording medium 10. The wavelength plate 122 is preferably a quarter wavelength plate based on the wavelength of the light emitted from the first light source 110. In the case of employing the wave plate 122 as described above, although the wavelength plate 122 can not sufficiently perform the use of the second light source 112, since the recording density of the recording medium 10 is low, There is no significant problem in the light efficiency.

The light control means 140 is disposed on the optical path between the first optical path changing means 120 and the recording medium 10 and controls the size of a light spot formed on each recording medium 10. [

As shown in FIG. 5, the light control unit 140 may include a hologram element 141 as a first embodiment. The hologram element 141 has a holographic pattern on one side of which light directed to the recording medium 10 can be diffracted and transmitted as 0-order light and +1-order light.

A second embodiment of the light control means 140 may include a variable diaphragm 143 as shown in FIG. The variable diaphragm 143 appropriately adjusts the transmissive area, that is, the numerical aperture of light incident on the light sources 110 and 112 side.

The opening diameter of the variable diaphragm 143 is adjusted to correspond to the thickness of the adopted disc. That is, the light in the central region is always passed, while the light in the peripheral region is selectively passed or blocked depending on the thickness of the employed disc. In this manner, since the size of the light spot can be adjusted by adjusting the opening diameter of the variable diaphragm, it is possible to employ compatible discs such as the CD family 10a and the DVD 10b.

A third embodiment of the light control means 140 will be described with reference to FIG.

As shown in the figure, the light control means 140 controls the first light control (hereinafter, referred to as " first light control ") of the predetermined shape to block light in the intermediate region 210 between the paraxial region 200 and the far axis region 220 of the objective lens 126 And a transparent member 145 having a surface 146 and transmitting light incident on a surface other than the first light control surface 146.

Here, the paraxial area 200 refers to a region around the lens center axis (optical axis) having a degree of spherical aberration that can be practically neglected, and the far axis area 220 refers to a region relatively closer to the optical axis than the paraxial area 200 And the middle area 210 means the area between the paraxial area 200 and the far axis area 220. [0033] FIG.

For example, when the numerical aperture (NA) of the objective lens 126 is 0.6, the first light control surface 146 is annular, and the position of the inner radius and the radius of the side thereof is 0.37 And the incident surface of the objective lens 126 having a numerical aperture of 0.4.

As shown in FIG. 8, a second light control surface 148 for blocking a part of the light passing through the far axis region 220 of the objective lens 126 is provided to the light control means 140, . When the numerical aperture of the objective lens 126 is 0.6, the second light control surface 148 has an annular shape in which the positions of the inner radius and the outer radius are between the numerical aperture 0.44 of the objective lens 126 and the numerical aperture 0.46 And may be formed on the transparent member 145 corresponding to the incident surface of the objective lens 126.

The first light control surface 146 and the second light control surface 148 may be provided by a total reflection coating formed on at least one surface of the transparent member 145.

The fourth embodiment of the light control means 140 controls the light passing through the intermediate region 210 in the light passing through the objective lens 126 as in the third embodiment, The light that is formed on at least one surface of the objective lens 126 and is incident on the intermediate region 210 of the objective lens 126 so as to be compatible with the recording medium 10 with different formats, And a first light control surface 149 for blocking or scattering at least a portion of the light that has passed through the region 210.

As shown in FIG. 10, the light control means 140 may be provided on at least one surface of the objective lens 126 to receive light incident on the far axis region 220 of the objective lens 126, And a second light control surface 150 blocking or scattering a portion of the light that has passed through the region 220.

Each of the first light control surface 149 and the second light control surface 150 may be provided on at least one surface of the objective lens 126 and may be provided by a total reflection coating of a predetermined shape to reflect incident light, Shaped annular groove, a stepped or wedge-shaped annular groove, or the like.

In this case as well, the width and position of the first light control surface 149 and the second light control surface 150 with respect to the numerical aperture of the objective lens 126 are the same as those described in the third embodiment of the light control means You can set it up like this.

The photodetector 130 receives the light reflected by the recording medium 10 and received via the objective lens 126 and the first optical path changing means 120 and converts the light into an electric signal, Detects an error signal and an information signal of the medium (10). The photodetector 130 includes a plurality of dividing plates capable of independently receiving light so that information and error signals can be detected by differential and summing. Since the photodetector 130 is widely known, a detailed description thereof will be omitted.

The interchangeable optical pickup apparatus according to the present invention further includes a collimating lens 124 for changing incident light on the optical path between the second optical path changing means 116 and the objective lens 126, . An astigmatic lens 128 may be further provided on the optical path between the first optical path changing means 120 and the photodetector 130 so as to detect a focus error signal by an astigmatism method. In addition, a grating 118 may further be provided between the second optical path changing means and the objective lens 126 so that a track error signal can be detected by a 3 beam beep.

As described above, the compatible optical pickup device includes two light sources, that is, a first light source 110 and a second light source 112, for emitting light of different wavelengths, and the recording medium 10 ), It is possible to fundamentally prevent the data from being destroyed during reproduction of the information recorded on the CD-R comprising the CD family, particularly the organic dye recording film layer. When the recording medium 10 including the light control means 140 is employed, the size of the light spot can be adjusted.

Claims (25)

A first optical path changing means for changing the traveling path of the incident light; a second optical path changing means disposed on the optical path between the first optical path changing means and the recording medium to form a light spot on the recording medium Light control means for adjusting the size of a light spot to be converged in the objective lens and formed on the recording medium, and means for receiving light passing through the objective lens and the first optical path changing means A first light source for emitting light of a predetermined wavelength to the light source; and a second light source for emitting light of a wavelength different from that of the first light source, And second light path changing means for changing the path of the incident light so that the light emitted from the first light source and the light emitted from the second light source arranged at different positions are provided to the recording medium Compatible optical pickup apparatus with. The liquid crystal display device according to claim 1, wherein the first light source is a semiconductor laser that emits light having a wavelength of 650 nm ± 20 nm, and the second light source is a semiconductor laser that emits light having a wavelength of 760 nm ± 20 nm Type optical pickup device. 3. The light source device according to claim 1 or 2, wherein the second light path changing means is configured to cause the light emitted from the first light source and the second light source to pass straight through and reflect the other light, Is directed to the first optical path changing means. ≪ Desc / Clms Page number 19 > 4. The compatible optical pickup apparatus according to claim 3, wherein the second optical path changing means is a beam splitter which transmits and reflects incident light at a predetermined light amount ratio. 4. The compatible optical pickup apparatus according to claim 3, wherein the second optical path changing means is a polarizing beam splitter which transmits incident light of a predetermined polarized light and reflects light of another polarized light. 3. The compatible optical pickup apparatus according to claim 1 or 2, wherein the first optical path changing means is a polarizing beam splitter which transmits light of a predetermined polarization among the incident light and reflects the remaining polarized light. 7. The compatible optical pickup apparatus of claim 6, further comprising a wave plate positioned on an optical path between the first optical path changing unit and the objective lens and changing the polarization direction of the incident light. The compatible optical pickup apparatus of claim 7, wherein the wave plate is a quarter wave plate based on light emitted from the first light source. 3. The optical pickup device according to claim 1 or 2, wherein the first optical path changing means guides the light incident from the second optical path changing means side to the recording medium, And a beam splitter for guiding the light beam to be directed toward the optical disc. 3. The optical pickup device according to claim 1 or 2, wherein the light control means is arranged on an optical path between the first optical path changing means and the objective lens and diffracts light directed to the recording medium into zero- Wherein the hologram element is a hologram element in which a hologram pantone for transmitting light is formed. 3. The optical pickup device according to claim 1 or 2, wherein the light control means is a variable diaphragm disposed on an optical path between the first optical path changing means and the objective lens and capable of adjusting a diameter of light directed to the recording medium Wherein the optical pickup device comprises: 3. The objective lens of claim 1 or 2, wherein the light control means is arranged on the optical path between the first optical path changing means and the objective lens, and the light in the intermediate region between the paraxial region and the far axis region of the objective lens Wherein the first optical control surface is a transparent member having a first light control surface of a predetermined shape for blocking light and transmitting light incident on the surface of the first light control surface. 13. The compatible optical pickup apparatus according to claim 12, wherein the transparent member further comprises a second light control surface for shielding a part of light passing through the far axis region of the objective lens. 14. The compatible optical pickup apparatus of claim 13, wherein each of the first light control surface and the second light control surface is provided by a total reflection coating formed on at least one surface of the transparent member. 14. The objective lens of claim 13, wherein the objective lens has a numerical aperture of 0.6, the first light control surface is annular, and each of the positions of the inner radius and the outer radius is between the numerical aperture of the objective lens of 0.37 and the numerical aperture of 0.4. And the second light control surface is annular and corresponds to the incident surface of the objective lens in which the positions of the inner radius and the outer radius are between the numerical aperture of the objective lens of 0.44 and the numerical aperture of 0.46 Wherein the transparent member is formed on the transparent member. 3. The objective lens of claim 1 or 2, wherein the light control means comprises a light blocking member which is formed on at least one surface of the objective lens and blocks or scatters at least part of light incident on the intermediate region of the objective lens or light passing through the intermediate region, 1 optical control surface. And a second light control surface formed on at least one surface of the objective lens for blocking or scattering light incident on the far axis region of the objective lens or part of the light passing through the far axis region, Wherein the optical pickup device further comprises: 18. The method of claim 17, wherein each of the first light control surface and the second light control surface is provided on at least one surface of the objective lens by a reflective coating of a predetermined shape adapted to reflect incident light. . 18. The objective lens of claim 17, wherein each of the first light control surface and the second light control surface is provided by a light control pattern formed on at least one surface of the objective lens so as to scatter or reflect incident light incident thereon To the optical pickup device. 20. The compatible optical pickup apparatus according to claim 19, wherein the light control pattern is an annular groove. 21. The compatible optical pickup apparatus according to claim 19 or 20, wherein the light control pattern is a V-shaped, protruding step-like or wedge-shaped. 18. The objective lens of claim 17, wherein the objective lens has a numerical aperture of 0.6, and the first light control surface is annular, and each of the positions of the inner radius and the outer radius is formed on an incident surface of the objective lens having a numerical aperture of 0.37 and a numerical aperture of 0.4 , And the second light control surface is formed on the incident surface of the objective lens, wherein the positions of the inner radius and the outer radius are between the numerical aperture 0.44 and the numerical aperture 0.46. The compatible optical pick-up apparatus according to claim 1 or 2, further comprising a collimating lens for converting incident light into parallel light on an optical path between the second optical path changing means and the objective lens. 3. The compatible optical pickup apparatus according to claim 1 or 2, further comprising an astigmatic lens on an optical path between the first optical path changing means and the photodetector. The optical system according to claim 1 or 2, further comprising a grating for diffracting incident light on the optical path between the second optical path changing means and the first optical path changing means to zero-order light, ± first-order light, The optical pickup device comprising: