JP2007172737A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a tracking error by making the diffracted light intensity ratio of a wavelength to be subjected to 3-beam division appropriate and increasing laser utilization efficiency in an optical pickup using optical beams of three different wavelengths. <P>SOLUTION: This pickup includes first to third light emitting parts for emitting optical beams of three different wavelengths, a first phase grating part 11a having a first phase height with respect to a reference surface, second phase grating parts 11b having second phase heights with respect to the reference surface on both sides of the first phase grating part thereby having 2-stage phase heights, a diffraction optical element 10 having a diffracted part 10a where optical beams emitted from the first to third light emitting parts are made incident while optical axes are aligned and the first to third optical beams are divided into 3 beams, an objective lens 7 for condensing the emitted optical beams on the signal recording surface of an optical disk 8, and a photodetector 10 for detecting return optical beams reflected on the optical disk 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup and an optical disc apparatus for recording and / or reproducing information on information recording media such as a plurality of types of optical discs using light beams having different three wavelengths.

  Conventionally, information signals are recorded and / or reproduced on a plurality of types of optical disks such as a CD (Compact Disc) using a light beam having a wavelength of about 785 nm and a DVD (Digital Versatile Disc) using a light beam having a wavelength of about 660 nm. There is a so-called two-wavelength optical pickup that performs the above.

  In recent years, in addition to this, a high-density recording optical disk capable of higher density recording using a light source having a wavelength of about 400 to 415 nm with a blue-violet semiconductor laser has been adopted. In providing an optical pickup compatible with these high-density recording optical disks, it is desired to have compatibility with optical disks of different formats such as conventional CD (Compact Disc) and DVD (Digital Versatile Disc).

  As an optical pickup having compatibility between optical discs of different formats, a configuration in which light beams of different wavelengths emitted from light emitting units provided in a plurality of light source units are condensed on a signal recording surface of each optical disc, or 1 There are those equipped with a configuration for condensing light beams of different wavelengths emitted from a plurality of light emitting units provided in one light source unit on the signal recording surface of each optical disc. In order to reduce the weight, it is necessary to share the optical elements by sharing the optical system of each wavelength.

  In general, as a method for obtaining a tracking error signal in an optical pickup, a diffraction grating is provided to obtain a tracking error signal by dividing a light beam emitted from a light source unit into three beams. There are a method, a differential push-pull (DPP) method, and a differential phase detection (DPD) method that obtains a tracking error signal with one beam without dividing the light beam.

  In the optical pickup having the above-mentioned compatibility, in order to obtain a tracking error signal, a diffraction grating is provided, and when generating three beams of a light beam of a certain wavelength, a light beam of another wavelength passes through this diffraction grating. There is a possibility that problems such as extremely low transmittance may occur.

  As an optical pickup that generates three beams for obtaining tracking signals with respect to light beams having different wavelengths, for example, an optical pickup disclosed in Japanese Patent Application Laid-Open No. 2003-6891 is known (see Patent Document 1).

  The optical pickup shown in Patent Document 1 includes a diffraction grating for two wavelengths. However, such an optical pickup is not compatible with an optical pickup that realizes three-wavelength compatibility, and a sufficient diffraction efficiency cannot be obtained.

  Furthermore, in the above-described optical pickup, the diffracted light intensity ratio, which is the light amount ratio between the 0th order light and the 1st order light having a wavelength that generates three beams, is also set within a predetermined range, and the 0th order light and ± 1st order light Although it is necessary to suppress the generation of other high-order diffracted light, it has not been possible with conventional optical pickups.

JP 2003-6891 A

  An object of the present invention is to provide an optical pickup that performs recording and / or reproduction on a plurality of types of optical disks using light beams having three different wavelengths, and that is used for primary light having a wavelength for performing three-beam division for tracking error detection. Provided is an optical pickup that can appropriately detect the tracking error for a plurality of types of optical disks by making the ratio of the diffracted light intensity of the 0th order light appropriate and improving the utilization efficiency of the light beam emitted from each light emitting section. There is to do.

To achieve this object, an optical pickup according to the present invention includes a first light emitting unit that emits a light beam having a first wavelength, a second light emitting unit that emits a light beam having a second wavelength, A third light emitting unit that emits a light beam having a wavelength of 3, a first phase grating unit having a first phase height with respect to the reference surface, and the reference surface on both sides of the first phase grating unit And a second phase grating portion having a second phase height, thereby having a two-stage phase height and the optical axis of the light beam emitted from the first to third light emitting portions. Diffractive optical elements having a diffractive portion that divides the first and third light beams into three beams, and the light beams emitted from the first to third light emitting portions are optical disc signals. An objective lens that focuses on the recording surface and a return light beam reflected by the optical disk are detected. And a light detector, the first wavelength is lambda _1, and the refractive index with respect to the first wavelength lambda ₁ of the diffractive optical element and the N _1, the first and second phase height, Both are 2 × λ ₁ / (N ₁ −1) or less.

  The optical pickup according to the present invention performs three-beam splitting for tracking error detection by a diffractive optical element when recording and / or reproducing with respect to a plurality of types of optical discs using light beams of three different wavelengths. Since three beams can be generated with an appropriate diffraction efficiency for a light beam of a wavelength, tracking error detection can be accurately performed for a plurality of types of optical disks by increasing the utilization efficiency of the light beam emitted from each light emitting unit. It can be carried out.

  Hereinafter, an optical pickup 1 to which the present invention is applied will be described with reference to the drawings.

  An optical pickup 1 to which the present invention is applied performs information recording / reproduction with respect to an optical disc, a spindle motor as a driving means for rotating the optical disc, and a feed for moving the optical pickup 1 in the radial direction of the optical disc. An optical disk device is configured together with a motor and the like. The optical pickup 1 records and reproduces information with respect to the optical disc rotated by a spindle motor. In addition, the optical pickup 1 and the optical disk apparatus using the optical pickup 1 are optical signals that realize compatibility among three standards for performing recording and / or reproduction with respect to a plurality of types of optical disks 8 having different formats by using light beams of three different wavelengths. A pickup and an optical disk device.

  The optical disk 8 used here is, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), a CD-R (Recordable) and a DVD-R (Recordable) that allow additional recording of information, and information can be rewritten. CD-RW (ReWritable), DVD-RW (ReWritable), DVD + RW (ReWritable), and other optical discs, and high-density recording using a semiconductor laser with a short emission wavelength of about 405 nm (blue-violet) It is a density recording optical disk, a magneto-optical disk, or the like.

  In particular, as the three types of optical discs in which information is reproduced or recorded by the optical disc apparatus 1 in the following, a high-density recording using a light beam having a protective substrate thickness of 0.1 mm and a wavelength of about 405 nm as recording / reproducing light is possible. A second optical disk such as a DVD that uses a light beam having a protective substrate thickness of 0.6 mm and a wavelength of about 660 nm as recording / reproducing light, and a light beam having a protective substrate thickness of 1.2 mm and a wavelength of about 785 nm. A description will be given on the assumption that a third optical disk such as a CD used as reproduction light is used.

  Also, in general, the tracking error signal generated by the optical pickup is different from a method in which detection is performed by dividing into three beams such as a three-spot method and a differential push-pull (DPP) method. There are a mixture of detection methods using one beam such as a phase detection (DPD (differential phase detection)) method, but the optical pickup 1 to which the present invention is applied selectively uses these detection methods. A description will be given assuming that a tracking error signal is generated.

  As shown in FIG. 1, an optical pickup 1 to which the present invention is applied includes a light source unit 3 that emits light beams of three different wavelengths, and a diffraction unit that transmits or divides the light beam emitted from the light source unit 3 into three beams. Diffractive optical element 4, a beam splitter 5 that reflects or transmits a light beam split or transmitted by diffractive optical element 4 and reflected light from optical disk 8, collimator lens 6, and light emitted from light source unit 3 A three-wavelength objective lens 7 for condensing the beam on the signal recording surface of the optical disc 8 and a plate-like optical element formed so as to guide the optical axis of the light beam of each wavelength reflected from the optical disc 8 to a predetermined photodetector. 9 and a photodetector 10 which is a common light receiving element for light beams of respective wavelengths, has a photodetector for signal detection, and detects a returning light beam reflected by the optical disk.

  The light source unit 3 includes a first light emitting unit that emits a light beam with a first wavelength of about 405 nm, a second light emitting unit that emits a light beam with a second wavelength of about 660 nm, and a wavelength of about 785 nm. And a third light emitting unit that emits a light beam of the third wavelength.

  That is, the light source unit 3 emits a laser diode of 405 nm band for a first optical disk that is a high-density recording optical disk and a laser beam of 660 nm band for a second optical disk such as a DVD. This is a so-called three-wavelength semiconductor laser element in which a laser diode and a laser diode that emits laser light in the 785 nm band to a third optical disk such as a CD are incorporated in one package.

  And the 1st thru | or 3rd light emission part of the light source part 3 is arrange | positioned so that a light beam can be radiate | emitted toward the same direction, Each light beam radiate | emitted from this 1st thru | or 3rd light emission part is And have a substantially common optical axis.

  In the optical pickup 1, the first to third light emitting units are configured to be disposed in the one light source unit 3. However, the present invention is not limited to this, and for example, the first to third light source units include the first to third light source units. The third light emitting units are arranged and arranged, and each light beam emitted from the first to third light emitting units arranged in these light source units is optically routed by an optical element such as a beam splitter as an optical path combining unit. May be combined so that each of the light beams has a common optical axis.

  The diffractive optical element 4 is provided between the light source unit 3 and the beam splitter 5, and includes a diffractive unit 4a that selectively splits the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. This is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The optical axes of the light beams having the first to third wavelengths emitted from the first to third light emitting units of the light source unit 3 are incident on the diffractive optical element 4 so as to be substantially coincident with each other. The unit 4a diffracts and emits a light beam having a first wavelength for a first optical disk such as a high-density recording optical disk into three beams composed of zero-order light and ± first-order light, and a second optical disk such as a DVD. The second wavelength light beam for transmission is transmitted and emitted, and the third wavelength light beam for a third optical disk such as a CD is diffracted and emitted into three beams composed of zero-order light and ± first-order light. Let Further, the diffractive optical element 4 converts the light beams of the first and third wavelengths into a light intensity ratio between the 0th order light and the ± 1st order light, that is, the diffracted light of the 0th order light with respect to the first order light. The beam is divided into three beams so that the intensity ratio (hereinafter also referred to as 0th-order light / 1st-order light diffracted light intensity ratio) is 3-10.

  The diffractive optical element 4 is divided into three beams by the diffractive portion 4a so that the 0th-order light / first-order light diffracted light intensity ratio of the light beams of the first and third wavelengths becomes 3 to 10 to be described later. As described above, the tracking error signal can be satisfactorily detected by the three divided beams, and the diffraction efficiency of the main beam can be kept high, so that the laser utilization efficiency can be increased.

  Here, the diffractive portion 4a is provided on the exit side surface of the diffractive optical element 4. However, the diffractive portion may be provided on the incident side surface, ie, the light source unit 3 side surface. Good. In addition, the diffractive portion 4a is provided on one surface of the diffractive optical element 4. However, the present invention is not limited to this, and the diffractive portion may be provided on both sides of the diffractive optical element. That is, for example, a first diffractive portion that is provided on the incident surface side and diffracts a light beam having at least one of the first to third wavelengths into three beams, and is provided on the output surface side. You may comprise so that it may have a 2nd diffraction part which diffracts the light beam of at least 1 wavelength among 3rd wavelengths into 3 beams.

  Specifically, when the light beam having the first wavelength of about 405 nm emitted from the first light emitting unit of the light source unit 3 is incident on the diffractive optical element 4, the diffractive unit 4 a causes zero-order light (hereinafter referred to as main light). And diffracted into three beams consisting of ± first-order light (hereinafter also referred to as sub-beams) and emitted to the beam splitter 5 side. Further, the light beam having the second wavelength of about 660 nm emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffractive unit 4a of the diffractive optical element 4 with an appropriate transmittance and is on the beam splitter 5 side. Is emitted. When the light beam having the third wavelength of about 785 nm emitted from the third light emitting unit of the light source unit 3 is incident on the diffractive optical element 4 as in the case of the light beam having the first wavelength, The beam is diffracted into three beams consisting of a main beam and two sub-beams at the section 4a and emitted to the beam splitter 5 side.

The diffractive portion 4a is formed by repeatedly forming a plurality of grating portions 11 having a fine grating pattern as shown in FIG. Each grid section 11 is formed in a substantially stepwise, in the first phase the height H ₁₁ with respect to the reference plane 11c, and the first phase grating portion 11a having a predetermined width W _11, the first in the second phase height H ₁₂ with respect to the reference plane 11c is formed stepwise on both sides of the phase grating portion 11a, and a second phase grating portions 11b having a predetermined width W _12. Incidentally, FIG. 2 in P ₁ shows a grating pitch, i.e., one pitch of the grating portion 11.

In the first and second phase grating portions 11a and 11b, the first and second phase heights H ₁₁ and H ₁₂ are not more than 2.00 times λ ₁ / (N ₁ −1), Phase height H ₁₁ is 0.01 times or more and 0.67 times or less of λ ₁ / (N ₁ -1) and 0.005 times or more and 0.34 times or less of λ ₃ / (N ₃ -1). And the second phase height H ₁₂ is 1.34 times or more and 2.00 times or less of λ ₁ / (N ₁ -1) and 0.66 times or more of λ ₃ / (N ₃ -1). The difference ΔH ₁ between the first phase height H ₁₁ and the second phase height H ₁₂ is 1.18 times or more and 1.36 times 1.36 times λ ₁ / (N ₁ −1). 2 times or less and 0.59 times or more and 0.68 times or less of λ ₃ / (N ₃ −1), and the second phase height H ₁₂ is higher than the first phase height H _11. Formed to meet the relationship It has been.

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 4. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 4.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 4. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₁ = 1.0, the width W ₁₁ = 0.804, and the width W ₁₂ = 0.064. In this case, the first phase height H ₁₁ = 370 nm and the second phase height H ₁₂ = 1470 nm.

That is, the first phase height H ₁₁ is 0.43 × λ ₁ / (N ₁ −1) and 0.21 × λ ₃ / (N ₃ −1), and the second phase height H 11 ₁₂ is 1.70 × λ ₁ / (N ₁ −1) and 0.85 × λ ₃ / (N ₃ −1), and the first phase height H ₁₁ and the second phase height H The difference ΔH _{1 from 12} is 1.28 × λ ₁ / (N ₁ −1) and 0.64 × λ ₃ / (N ₃ −1), and the second phase height H ₁₂ is the first and has a higher relationship than the phase height H _11.

  The diffractive optical element 4 having such a diffractive portion 4a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 4a has a diffraction efficiency of 53.1% for the 0th order light (main beam) and a diffraction efficiency of 7.7% for the ± 1st order light (sub beam) with respect to the light beam of the first wavelength. The 0th-order light / 1st-order diffracted light intensity ratio, which is the diffracted light intensity ratio of the main beam to the sub-beam, is 6.9, and the 0th-order light diffraction efficiency 56. The diffraction efficiency of ± 1st order light is 8.4%, and the 0th / first order diffracted light intensity ratio is 6.8. Further, the diffraction portion 4a has a transmittance for the second wavelength, that is, the diffraction efficiency of the 0th-order light is 69.7%, the diffraction efficiency of the ± 1st-order light is 6.5%, and a sufficient transmission near 70%. Rate is obtained.

  As described above, the diffractive optical element 4 has a high diffraction efficiency of the 0th order light and the 0th order light with respect to the light beams of the first and third wavelengths that are divided into three beams for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  According to the optical pickup 1 including the diffractive optical element 4 as described above, the diffractive optical element is used when detecting a tracking error signal when reproducing a plurality of types of optical disks using light beams having different three wavelengths. The four diffracting sections 4a can generate three beams with optimal diffraction efficiency for the first and third wavelength light beams that are divided into three beams, and the light beams with the wavelengths that are not subjected to the three beam division. Since the light can be transmitted with an appropriate transmittance, the laser utilization efficiency of the light beams of the respective wavelengths emitted from the first to third light emitting units of the light source unit 3 is increased, and the light beams of the respective wavelengths are used. Tracking error detection with high accuracy.

The tracking error signal detection using the diffractive optical element 4 employs a differential push-pull (DPP) method when the first wavelength is used, and differential phase detection (when the second wavelength is used). When a third wavelength is used, a three-spot method is adopted. As shown in FIGS. 3A and 3B, the diffractive optical element 4 condenses the main spot of the main beam on the track of the optical disk 8 on the signal recording surface of the optical disk 8 to perform differential push. pull (DPP) method is focused so as to be offset by a half of a track pitch P ₁ in the radial direction of the optical disc 8 (P _1/2) across the two sub-spots main spot of the sub beam in both sub-beams in the three-spot method sub spots in the radial direction of the optical disc 8 across the main spot by 1/4 of the track pitch P ₃ (P _3/4) is condensed so as to shift. Then, the main spot and both sub-spots are received by a photodetector of the photodetector 10 to be described later to detect a tracking error signal, and the objective lens 7 is moved in the tracking direction. In FIG. 3A and FIG. 3B, S _{10 to} S ₁₂ and S _{30 to} S ₃₂ indicate the spots of the diffracted light beams of the respective light beams on the signal recording surface of each optical disc. Yes, S ₁₀ is the 0th-order light of the first wavelength, S ₁₁ and S ₁₂ are the ± 1st-order light of the first wavelength, S ₃₀ is the 0th-order light of the third wavelength, S ₃₁ and S ₃₂ Indicates ± first order light of the third wavelength.

  Here, the photodetector 10 has a photodetector as a common light receiving element that receives the light beams of the first to third wavelengths, that is, the main beams of the second and third wavelengths are irradiated as will be described later. A first light receiving surface 14, second and third light receiving surfaces 15, 16 irradiated with a third wavelength sub beam, and a fourth light receiving surface 17 irradiated with a first wavelength main beam, And the fifth and sixth light receiving surfaces 18 and 19 irradiated with the sub-beam of the first wavelength, and the second and third light receiving surfaces 15 and 16 are arranged with the first light receiving surface 14 interposed therebetween. The fifth and sixth light receiving surfaces 18 and 19 are arranged with the fourth light receiving surface 17 interposed therebetween (see FIG. 4).

  The light beam emitted after being divided into three or transmitted by the diffractive optical element 4 is irradiated onto the signal recording surface of the optical disk 8 through the beam splitter 5, the collimator lens 6 and the objective lens 7 for three wavelengths, and the reflected light is plate-shaped. Light is received by the photodetector of the photodetector 10 through the optical element 9 and detected.

  The beam splitter 5 is disposed on the optical path between the diffractive optical element 4 and the collimator lens 6, and has a half mirror surface 5 a on the side close to the light source unit 3. The beam splitter 5 reflects the light beam divided and transmitted by the diffractive optical element 4 and emitted to the optical disc 8 side by the half mirror surface 5a. The beam splitter 5 transmits the return light beam reflected by the optical disc 8 and makes it incident on the plate-like optical element 9. That is, the beam splitter 5 is an optical element that branches the optical path of the return light beam from the optical path of the forward light beam.

  The collimator lens 6 is disposed between the beam splitter 5 and the objective lens 7 and converts the light beam reflected by the beam splitter 5 into parallel light. The three-wavelength objective lens 7 focuses the light beams having the first to third wavelengths on the signal recording surface of the optical disc 8, respectively.

  The plate-like optical element 9 is disposed between the beam splitter 5 and the photodetector 10, and returns the light beams having the first to third wavelengths reflected by the optical disc 8 and transmitted through the beam splitter 5 to the photodetector. It consists of a diffraction grating that is incident on the light receiving surface of 10 photodetectors. The plate-like optical element 9 diffracts or transmits the optical axes of the first to third wavelength light beams reflected by the optical disc 8 so as to reach the light receiving surface of a desired photodetector of the photodetector 10. That is, the plate-like optical element 9 emits light beams having the first to third wavelengths returned from the first to third light emitting units of the light source unit 3 and reflected by the optical disc via the optical components described above. This corrects a slight deviation of the optical path and leads it to a desired position of the photodetector of the photodetector 10.

The photodetector of the photodetector 10 in which the light beam having the first to third wavelengths is incident on the desired position by the plate-like optical element 9 is a common light receiving element for returning light of three wavelengths as shown in FIG. The first light receiving surface 14 on which the second and third wavelength zero-order light is incident and the first light-receiving surface 14 are sandwiched, and the third wavelength ± first-order light having the third wavelength is incident. The second and third light receiving surfaces 15 and 16, the fourth light receiving surface 17 on which the 0th-order light of the first wavelength is incident, and the fourth light receiving surface 17 are sandwiched between the first and second light receiving surfaces 17 and 16. It has fifth and sixth light receiving surfaces 18 and 19 on which ± 1st order light divided into three is incident. The first light receiving surface 14 and the fourth light receiving surface 17 are formed with light receiving portions A1, B1, C1, and D1, and light receiving portions A2, B2, C2, and D2, which are divided into four parts, respectively, for generating digital signals. A focus error signal for generating an RF signal and a focusing servo signal is detected. The second and third light receiving surfaces 15, 16 and the fifth and sixth light receiving surfaces 18, 19 are divided into two light receiving portions E1, F1, light receiving portions G1, H1, light receiving portions E2, F2 and light receiving portions, respectively. Portions G2 and H2 are formed to detect a tracking error signal for generating a tracking servo signal. In FIG. 4, S _{13 to} S ₁₅ , S ₂₃ , and S _{33 to} S ₃₅ indicate spots of diffracted light of light beams of respective wavelengths on the respective light receiving surfaces, and S ₁₃ is the first S ₁₄ and S ₁₅ are ± first order light of the first wavelength, S ₂₃ is the 0th order light of the second wavelength, S ₃₃ is the 0th order light of the third wavelength, S ₃₄ and S ₃₅ indicate ± first-order light of the third wavelength.

  In order to detect the tracking error signal by the photodetector 10, the outputs from the light receiving portions A1 to H1 and A2 to H2 of the first to sixth light receiving surfaces 14 to 19 are respectively SA1, SB1, SC1, SD1, SE1, SF1, SG1, SH1, SA2, SB2, SC2, SD2, SE2, SF2, SG2, SH2, and the above-described differential push-pull (DPP) method, differential phase detection (DPD) method, and three-beam method The tracking error signal TE can be obtained as appropriate. Specifically, the differential push-pull (DPP) tracking error signal using the first wavelength is TE = ((SA2 + SB2) − (SC2 + SD2)) − k × ((SE2−SF2) − (SG2−). SH2)). Here, k is a value determined so as to remove the offset of TE. Further, a tracking error signal of the differential phase detection (DPD) method using the second wavelength can be obtained by TE = (SA1 + SC1) − (SB1 + SD1). Further, a tracking error signal of the three beam system using the third wavelength can be obtained by TE = (SE1 + SF1) − (SG1 + SH1).

  Hereinafter, the operation of the optical pickup 1 will be described. The optical pickup 1 emits a light beam having a first wavelength from the first light emitting unit of the light source unit 3 when the first optical disc is mounted as the optical disc 8. The light beam having the first wavelength is diffracted by the diffractive portion 4a of the diffractive optical element 4 so that the zero-order light and the ± first-order light are within the proper range of the 0th-order light / 1st-order light diffracted light intensity ratio of about 3-10. Diffracted into three beams with light. At this time, generation of high-order diffracted light can be reduced to an extent that does not adversely affect the generation.

  The optical pickup 1 emits a light beam having the second wavelength from the second light emitting unit of the light source unit 3 when a second optical disc is mounted as the optical disc 8. The light beam of the second wavelength is transmitted with an appropriate transmittance by the diffractive portion 4a of the diffractive optical element 4. At this time, generation of high-order diffracted light can be reduced to an extent that does not adversely affect the generation.

  The optical pickup 1 emits a light beam having a third wavelength from the third light emitting unit of the light source unit 3 when a third optical disc is mounted as the optical disc 8. This light beam of the third wavelength is combined with the 0th order light and the ± 1st order by the diffractive portion 4a of the diffractive optical element 4 within a proper range where the 0th order light / 1st order light diffracted light intensity ratio is about 3-10. Diffracted into 3 beams with light. At this time, generation of high-order diffracted light can be reduced to an extent that does not adversely affect the generation.

  When the light beams having the first to third wavelengths emitted from the diffractive optical element 4 are irradiated onto the half mirror surface 5 a of the beam splitter 5, the light beams are raised to the optical disk 8 side and are collimated by the collimator lens 6. . Next, the light beam is condensed on the signal recording surface of the optical disk 8 by the objective lens 7, and a light spot is formed by the main beam and the sub beam as shown in FIG.

  At this time, the main spot by the zero-order light is formed on the track, and the sub-spot by the ± first-order light is, as described above, in the radial direction of the optical disk 8 by half the track pitch in the differential push-pull (DPP) method. The three-spot method is formed at a position shifted in the radial direction of the optical disk 8 by 1/4 of the track pitch.

  The return light beam reflected by the signal recording surface of the optical disk 8 passes through the beam splitter 5 and enters the plate-like optical element 9, and the main beams of the second and third wavelengths are incident on the first light receiving surface 14. Condensed, or a main beam of the first wavelength is condensed on the fourth light receiving surface 17, and a sub beam of the third wavelength is condensed on the second and third light receiving surfaces 15, 16, or the first Are subtracted or transmitted so as to be focused on the fifth and sixth light receiving surfaces 18 and 19. At this time, the plate-like optical element 9 diffracts or transmits the optical axis of the light beam having the first to third wavelengths so as to guide it to a desired position.

  The optical pickup 1 detects spot light irradiated on the first to sixth light receiving surfaces 14 to 19 of the photodetector 10 to thereby detect an RF signal for recording or reproducing an information signal and a tracking error signal for tracking control. Is detected.

  At this time, the optical pickup 1 maintains a high amount of zero-order light that requires high power, and sets the ratio of the 0th-order light / first-order light diffracted light intensity ratio of the light beam having the wavelength for performing the three-beam splitting to an appropriate range. In addition, the utilization efficiency of the laser emitted from the light source unit 3 can be improved, and the tracking error signal by three beams can be detected with high accuracy.

  The optical pickup 1 to which the present invention is applied has three beams for detecting a tracking error by a diffractive optical element when recording and / or reproducing with respect to a plurality of types of optical disks using light beams of three different wavelengths. Since three beams can be generated with an appropriate diffraction efficiency for a light beam having a wavelength to be split, and a light beam having a wavelength not to be split can be transmitted with an appropriate transmittance. The laser utilization efficiency of the light beam emitted from each light emitting unit can be increased, and tracking error detection can be accurately performed for a plurality of types of optical disks.

  Further, the optical pickup 1 to which the present invention is applied has optical paths of light beams with different three wavelengths that are selectively emitted from the first to third light emitting units of the light source unit 3 according to the format type of the optical disc 8. Since tracking error detection can be performed appropriately for optical discs with different formats in common, it is possible to read and write good signals for multiple types of optical discs, and to improve the efficiency of laser use. As a result, downsizing and compatibility with a plurality of types of optical disks are realized.

  In the optical pickup to which the present invention is applied, the diffractive optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 20 is provided between the light source unit 3 and the beam splitter 5 and selectively divides the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 20a of the diffractive optical element 20 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams of the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 20, the diffractive unit 20a generates zero-order light and ± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. Further, the light beam of the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffractive unit 20a of the diffractive optical element 20 and is emitted to the beam splitter 5 side.

The first diffraction grating 20a includes a plurality of grating portions 21 each having a fine grating pattern as shown in FIG. Each grid section 21 is formed in a substantially stepwise, in the first phase the height H ₂₁ with respect to the reference plane 21c, and the first phase grating portion 21a having a predetermined width W _21, the first in the second phase height H ₂₂ against stepwise formed reference plane 21c on both sides of the phase grating portion 21a, and a second phase grating portions 21b having a predetermined width W _22. Incidentally, in FIG. 5 P ₂ is a grating pitch of each grating portion 21, that is, shows one pitch.

In the first phase grating portions 21a and 21b, the first and second phase heights H ₂₁ and H ₂₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₂₁ is not less than 0.99 times and not more than 1.36 times λ ₁ / (N ₁ -1) and not less than 0.49 times and not more than 0.68 times λ ₃ / (N ₃ -1); The second phase height H ₂₂ is 1.55 times or more and 2.00 times or less of λ ₁ / (N ₁ −1) and 0.77 times or more and 1.00 of λ ₃ / (N ₃ −1). The difference ΔH ₂ between the first phase height H ₂₁ and the second phase height H ₂₂ is 0.44 times or more and 0.67 times or less of λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is 0.21 times or more and 0.34 times or less and satisfies the relationship that the second phase height H ₂₂ is higher than the first phase height H _21. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 20. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 20.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 20. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₂ = 1.0, the width W ₂₁ = 0.796, and the width W ₂₂ = 0.072. In this case, the first phase height H ₂₁ = 920 nm and the second phase height H ₂₂ = 1360 nm.

That is, the first phase height H ₂₁ is 1.07 × λ ₁ / (N ₁ −1) and 0.53 × λ ₃ / (N ₃ −1), and the second phase height H _{21 22} is 1.58 × λ ₁ / (N ₁ −1) and 0.79 × λ ₃ / (N ₃ −1), and the first phase height H ₂₁ and the second phase height H The difference ΔH ₂ with respect to ₂₂ is 0.51 × λ ₁ / (N ₁ −1) and 0.25 × λ ₃ / (N ₃ −1), and the second phase height H ₂₂ is the first and has a higher relationship than the phase height H _21.

  The diffractive optical element 20 having such a diffractive portion 20a diffracts the light beam having the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 20a has a diffraction efficiency of 0th order light of 50.1% and a diffraction efficiency of ± 1st order light of 7.2% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 7.0, and the diffraction efficiency of the 0th order light is 56.1% and the diffraction efficiency of ± 1st order light is 8.4% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 6.7. Further, the diffraction section 20a has a diffraction efficiency of 0th-order light with respect to the second wavelength of 53.4% and a diffraction efficiency of ± 1st-order light of 10.3%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 20 has a high zero-order diffraction efficiency for the first and third wavelength light beams that are divided into three beams for tracking error detection, and at the same time, The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 30 is provided between the light source unit 3 and the beam splitter 5 and selectively divides the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 30a of the diffractive optical element 30 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams of the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 30, the diffractive unit 30 a causes the zero-order light and ± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. The light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 30a of the diffractive optical element 30 and is emitted to the beam splitter 5 side.

The first diffraction grating 30a is formed by repeatedly forming a plurality of grating portions 31 having a fine grating pattern as shown in FIG. 6 as one pitch. Each grid section 31 is formed in a substantially stepwise, in the first phase the height H ₃₁ with respect to the reference plane 31c, and the first phase grating portion 31a having a predetermined width W _31, the first in the second phase height H ₃₂ with respect to the reference plane 31c is formed stepwise on both sides of the phase grating portion 31a, and a second phase grating portions 31b having a predetermined width W _32. Incidentally, FIG. 6 in P ₃ is the grating pitch of each grating portion 31, that is, shows one pitch.

In the first phase grating portions 31a and 31b, the first and second phase heights H ₃₁ and H ₃₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₃₁ is not less than 0.88 times and not more than 1.20 times λ ₁ / (N ₁ -1), and not less than 0.43 times and not more than 0.60 times λ ₃ / (N ₃ -1); The second phase height H ₃₂ is 1.14 to 1.63 times λ ₁ / (N ₁ −1) and 0.57 to 0.82 times λ ₃ / (N ₃ −1). The difference ΔH ₃ between the first phase height H ₃₁ and the second phase height H ₃₂ is not less than 0.23 times and not more than 0.42 times λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is 0.11 or more and 0.21 or less and satisfies the relationship that the second phase height H ₃₂ is higher than the first phase height H _31. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 30. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 30.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.600 as the material of the diffractive optical element 30. When a glass mold glass material having a refractive index N ₃ with respect to 783 nm of 1.576 is used, the grating pitch P ₃ = 1.0, the width W ₃₁ = 0.548, and the width W ₃₂ = 0. When 180, the first phase height H ₃₁ = 710 nm and the second phase height H ₃₂ = 870 nm.

That is, the first phase height H ₃₁ is 1.05 × λ ₁ / (N ₁ −1) and 0.52 × λ ₃ / (N ₃ −1), and the second phase height H _{31 32} is 1.29 × λ ₁ / (N ₁ −1) and 0.64 × λ ₃ / (N ₃ −1), and the first phase height H ₃₁ and the second phase height H The difference ΔH ₃ with respect to ₃₂ is 0.24 × λ ₁ / (N ₁ −1) and 0.12 × λ ₃ / (N ₃ −1), and the second phase height H ₃₂ is the first and has a higher relationship than the phase height H _31.

  The diffractive optical element 30 having such a diffractive portion 30a diffracts a light beam having the first and third wavelengths into a main beam and two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 30a has a diffraction efficiency of 55.1% for the 0th order light and a diffraction efficiency of ± 1st order light of 8.2% for the light beam of the first wavelength. The diffracted light intensity ratio is 6.7, and the zero-order light diffraction efficiency is 58.8% and the ± first-order light diffraction efficiency is 8.4% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 7.0. In addition, the diffraction section 30a has a diffraction efficiency of 0th order light with respect to the second wavelength of 62.4% and a diffraction efficiency of ± 1st order light of 11.3%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 30 has a high diffraction efficiency of the 0th order light and the 0th order light with respect to the light beams of the first and third wavelengths that are divided into three beams for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 40 is provided between the light source unit 3 and the beam splitter 5, and diffractive unit 40 a that selectively splits the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 40a of the diffractive optical element 40 diffracts the light beam of the first wavelength for the first optical disc into three beams, transmits the light beam of the second wavelength for the second optical disc, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams having the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 40, the diffractive unit 40a generates zero-order light and ±± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. The light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 40a of the diffractive optical element 40 and is emitted to the beam splitter 5 side.

The first diffraction grating 40a is formed by repeatedly forming a plurality of grating portions 41 having a fine grating pattern as shown in FIG. Each grating part 41 is formed in a substantially stepped cross section, and has a first phase grating part 41a having a first phase height H ₄₁ and a predetermined width W ₄₁ with respect to the reference surface 41c. in the second phase height H ₄₂ with respect to the reference plane 41c is formed stepwise on both sides of the phase grating portion 41a, and a second phase grating portions 41b having a predetermined width W _42. In FIG 7 P ₄ is the grating pitch of each grating portion 41, that is, shows one pitch.

In the first phase grating portions 41a and 41b, the first and second phase heights H ₄₁ and H ₄₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₄₁ is not less than 0.63 times and not more than 1.10 times λ ₁ / (N ₁ -1) and not less than 0.31 times and not more than 0.55 times λ ₃ / (N ₃ -1); second phase height _{H 42 is, λ 1 / (N 1 -1} ) of 0.49 times to 0.85 times or less, and λ ₃ / _{(N 3} -1) of 0.24 times 0.42 The difference ΔH ₄ between the first phase height H ₄₁ and the second phase height H ₄₂ is not less than 0.03 times and not more than 0.32 times λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is not less than 0.01 times and not more than 0.16 times, and satisfies the relationship that the first phase height H ₄₁ is higher than the second phase height H _42. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the material constituting the diffractive optical element 40. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 40.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 40. When a glass glass material having a refractive index N ₃ with respect to 783 nm is 1.454, the grating pitch P ₄ = 1.0, the width W ₄₁ = 0.656, and the width W ₄₂ = 0.092. In this case, the first phase height H ₄₁ = 570 nm and the second phase height H ₄₂ = 470 nm.

That is, the first phase height H ₄₁ is 0.66 × λ ₁ / (N ₁ −1) and 0.33 × λ ₃ / (N ₃ −1), and the second phase height H _{41 42} is 0.54 × λ ₁ / (N ₁ −1) and 0.27 × λ ₃ / (N ₃ −1), and the first phase height H ₄₁ and the second phase height H The difference ΔH _{4 from 42} is 0.12 × λ ₁ / (N ₁ −1) and 0.06 × λ ₃ / (N ₃ −1), and the first phase height H ₄₁ is the second and has a higher relationship than the phase height H _42.

  The diffractive optical element 40 having such a diffractive portion 40a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / 1st-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 40a has a diffraction efficiency of 0th order light of 50.2% and a diffraction efficiency of ± 1st order light of 7.3% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 6.8, and the diffraction efficiency of the 0th order light is 60.6% and the diffraction efficiency of ± 1st order light is 8.8% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 6.9. Further, the diffraction section 40a has a diffraction efficiency of 0th-order light with respect to the second wavelength of 51.5% and a diffraction efficiency of ± 1st-order light of 10.4%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 40 has a high 0th-order light diffraction efficiency for the first and third wavelength light beams that are split into three beams for tracking error detection, and at the same time, The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 50 is provided between the light source unit 3 and the beam splitter 5, and diffractive unit 50 a that selectively splits the first to third wavelength light beams emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 50a of the diffractive optical element 50 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams of the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 50, the diffractive unit 50a generates zero-order light and ±± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. The light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 50a of the diffractive optical element 50 and is emitted to the beam splitter 5 side.

The first diffraction grating 50a is formed by repeatedly forming a plurality of grating portions 51 having a fine grating pattern as shown in FIG. 8 as one pitch. Each grating part 51 is formed in a substantially stepped cross section, and has a first phase grating part 51a having a first phase height H ₅₁ and a predetermined width W ₅₁ with respect to the reference plane 51c. in the second phase height H ₅₂ against stepwise formed reference plane 51c on both sides of the phase grating portion 51a, and a second phase grating portions 51b having a predetermined width W _52. Incidentally, P ₅ in FIG. 8, the grating pitch of each grating portion 51, that is, shows one pitch.

In the first phase grating portions 51a and 51b, the first and second phase heights H ₅₁ and H ₅₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₅₁ is not less than 0.83 times and not more than 1.13 times λ ₁ / (N ₁ -1) and not less than 0.41 times and not more than 0.57 times λ ₃ / (N ₃ -1); The second phase height H ₅₂ is not less than 0.58 times and not more than 0.86 times λ ₁ / (N ₁ −1) and not less than 0.28 times and 0.43 times λ ₃ / (N ₃ −1). The difference ΔH ₅ between the first phase height H ₅₁ and the second phase height H ₅₂ is not less than 0.22 times and not more than 0.42 times λ ₁ / (N ₁ −1), In addition, λ ₃ / (N ₃ −1) is 0.10 times or more and 0.21 times or less and satisfies the relationship that the first phase height H ₅₁ is higher than the second phase height H _52. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 50. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 50.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 50. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₅ = 1.0, the width W ₅₁ = 0.528, and the width W ₅₂ = 0.192. In this case, the first phase height H ₅₁ = 950 nm and the second phase height H ₅₂ = 720 nm.

That is, the first phase height H ₅₁ is 1.10 × λ ₁ / (N ₁ −1) and 0.55 × λ ₃ / (N ₃ −1), and the second phase height H _{51 52} is 0.83 × λ ₁ / (N ₁ −1) and 0.42 × λ ₃ / (N ₃ −1), and the first phase height H ₅₁ and the second phase height H The difference ΔH ₅ with respect to ₅₂ is 0.27 × λ ₁ / (N ₁ −1) and 0.13 × λ ₃ / (N ₃ −1), and the first phase height H ₅₁ is the second It has a higher relation than the phase height H _52.

  The diffractive optical element 50 having such a diffractive portion 50a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffractive portion 50a has a diffraction efficiency of 50.1% for the 0th order light and a diffraction efficiency of 15.2% for the ± 1st order light with respect to the first wavelength light beam. The diffracted light intensity ratio is 3.3, and the diffraction efficiency of the 0th order light is 55.9% and the diffraction efficiency of ± 1st order light is 8.1% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 6.9. In addition, the diffraction section 50a has a diffraction efficiency of 0th order light of 53.4% with respect to the second wavelength and a diffraction efficiency of ± 1st order light of 7.2%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 50 has a high zero-order light diffraction efficiency and a zero-order light at the same time with respect to the first and third wavelength light beams that are divided into three beams for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 60 is provided between the light source unit 3 and the beam splitter 5 and selectively divides the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 60a of the diffractive optical element 60 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disc is diffracted into three beams.

  Specifically, when the light beams having the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 60, the diffractive unit 60a generates zero-order light and ± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. Further, the light beam of the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffractive unit 60a of the diffractive optical element 60 and is emitted to the beam splitter 5 side.

The first diffraction grating 60a is formed by repeatedly forming a plurality of grating portions 61 having a fine grating pattern as shown in FIG. Each grating part 61 is formed in a substantially stepped cross section, and has a first phase grating part 61a having a first phase height H ₆₁ and a predetermined width W ₆₁ with respect to the reference surface 61c. in the second phase height H ₆₂ with respect to the reference plane 61c is formed stepwise on both sides of the phase grating portion 61a, and a second phase grating portions 61b having a predetermined width W _62. In FIG. 9, P ₆ indicates the lattice pitch of each lattice portion 61, that is, 1 pitch.

In the first phase grating portions 61a and 61b, the first and second phase heights H ₆₁ and H ₆₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height H ₆₁ is not less than 0.63 times and not more than 0.69 times λ ₁ / (N ₁ -1), and is not less than 0.31 times and not more than 0.35 times λ ₃ / (N ₃ -1), second phase height _{H 62 is, λ 1 / (N 1 -1} ) of 0.03 times to 0.20 times or less, and λ ₃ / _{(N 3} -1) of 0.01 times to 0.10 The difference ΔH ₆ between the first phase height H ₆₁ and the second phase height H ₆₂ is 0.49 times or more and 0.63 times or less of λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is 0.24 times or more and 0.31 times or less and satisfies the relationship that the first phase height H ₆₁ is higher than the second phase height H _62. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 60. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 60.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ for 405 nm is 1.470 as the material of the diffractive optical element 60. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₆ = 1.0, the width W ₆₁ = 0.176, and the width W ₆₂ = 0.088. In this case, the first phase height H ₆₁ = 550 nm and the second phase height H ₆₂ = 40 nm.

That is, the first phase height H ₆₁ is 0.64 × λ ₁ / (N ₁ −1) and 0.32 × λ ₃ / (N ₃ −1), and the second phase height H _{61 62} is 0.05 × λ ₁ / (N ₁ −1) and 0.02 × λ ₃ / (N ₃ −1), and the first phase height H ₆₁ and the second phase height H The difference ΔH _{6 from 62} is 0.59 × λ ₁ / (N ₁ −1) and 0.30 × λ ₃ / (N ₃ −1), and the first phase height H ₆₁ is the second and has a higher relationship than the phase height H _62.

  The diffractive optical element 60 having such a diffractive portion 60a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / 1st-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 60a has a diffraction efficiency of 0th order light of 50.0% and a diffraction efficiency of ± 1st order light of 8.7% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 5.7, and the diffraction efficiency of the 0th order light is 59.5% and the diffraction efficiency of ± 1st order light is 8.5% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 7.0. Further, the diffraction section 60a has a diffraction efficiency of 0th order light with respect to the second wavelength of 50.1% and a diffraction efficiency of ± 1st order light of 10.3%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 60 has a high diffraction efficiency of the 0th order light and the 0th order light with respect to the light beams of the first and third wavelengths that perform the 3-beam splitting for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 70 is provided between the light source unit 3 and the beam splitter 5 and selectively divides the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 70a of the diffractive optical element 70 diffracts the light beam of the first wavelength for the first optical disc into three beams, transmits the light beam of the second wavelength for the second optical disc, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams of the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 70, the diffractive unit 70a generates zero-order light and ±± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. The light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 70a of the diffractive optical element 70 and is emitted to the beam splitter 5 side.

The first diffraction grating 70a is formed by repeatedly forming a plurality of grating portions 71 having a fine grating pattern as shown in FIG. 10 as one pitch. Each grating part 71 is formed in a substantially stepped cross section, and has a first phase grating part 71a having a first phase height H ₇₁ and a predetermined width W ₇₁ with respect to the reference plane 71c. in the second phase height H ₇₂ against stepwise formed reference plane 71c on both sides of the phase grating portion 71a, and a second phase grating portions 71b having a predetermined width W _72. Incidentally, FIG. 10 in P ₇ is the grating pitch of each grating portion 71, that is, shows one pitch.

In the first phase grating portions 71a and 71b, the first and second phase heights H ₇₁ and H ₇₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₇₁ is 1.26 times to 1.36 times λ ₁ / (N ₁ -1) and 0.63 times to 0.68 times λ ₃ / (N ₃ -1); The second phase height H ₇₂ is 1.33 times or more and 1.53 times or less of λ ₁ / (N ₁ −1) and 0.66 times or more and 0.76 of λ ₃ / (N ₃ −1). The difference ΔH ₇ between the first phase height H ₇₁ and the second phase height H ₇₂ is not less than 0.01 times and not more than 0.24 times λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is not less than 0.005 times and not more than 0.12 times, and satisfies the relationship that the second phase height H ₇₂ is higher than the first phase height H _71. Is formed as .

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 70. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 70.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 70. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₇ = 1.0, the width W ₇₁ = 0.584, and the width W ₇₂ = 0.116. In this case, the first phase height H ₇₁ = 1140 nm and the second phase height H ₇₂ = 1210 nm are set.

That is, the first phase height H ₇₁ is 1.32 × λ ₁ / (N ₁ −1) and 0.66 × λ ₃ / (N ₃ −1), and the second phase height H _{71 72} is 1.40 × λ ₁ / (N ₁ −1) and 0.70 × λ ₃ / (N ₃ −1), and the first phase height H ₇₁ and the second phase height H The difference ΔH _{7 from 72} is 0.08 × λ ₁ / (N ₁ −1) and 0.04 × λ ₃ / (N ₃ −1), and the second phase height H ₇₂ is the first The phase height is higher than H ₇₁ .

  The diffractive optical element 70 having such a diffractive portion 70a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. In other words, the diffraction unit 70a has a diffraction efficiency of 0th order light of 50.2% and a diffraction efficiency of ± 1st order light of 7.9% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 6.3, and the diffraction efficiency of the 0th order light is 55.0% and the diffraction efficiency of ± 1st order light is 10.6% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 5.2. Further, the diffraction section 70a has a diffraction efficiency of 0th order light with respect to the second wavelength of 78.7% and a diffraction efficiency of ± 1st order light of 6.2%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 70 has a high zero-order diffraction efficiency at the same time as the zero-order light with respect to the first and third wavelength light beams that are split into three beams for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 80 is provided between the light source unit 3 and the beam splitter 5, and diffractive unit 80 a that selectively splits the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 80a of the diffractive optical element 80 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams having the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 80, the diffractive unit 80a generates zero-order light and ±± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. The light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 80a of the diffractive optical element 80 and is emitted to the beam splitter 5 side.

The first diffraction grating 80a is formed by repeatedly forming a plurality of grating portions 81 having a fine grating pattern as shown in FIG. Each grid section 81 is formed in a substantially stepwise, in the first phase the height H ₈₁ with respect to the reference plane 81c, and the first phase grating portion 81a having a predetermined width W _81, the first in the second phase height H ₈₂ against stepwise formed reference plane 81c on both sides of the phase grating portion 81a, and a second phase grating portions 81b having a predetermined width W _82. Incidentally, FIG. 11 in P ₈ is the grating pitch of each grating portion 81, that is, shows one pitch.

In the first phase grating portions 81a and 81b, the first and second phase heights H ₈₁ and H ₈₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height H ₈₁ is 1.65 times or more and 1.75 times or less of λ ₁ / (N ₁ -1) and 0.82 times or more and 0.87 times or less of λ ₃ / (N ₃ -1), The second phase height H ₈₂ is 1.18 times or more and 1.25 times or less of λ ₁ / (N ₁ −1) and 0.59 times or more and 0.62 of λ ₃ / (N ₃ −1). The difference ΔH ₈ between the first phase height H ₈₁ and the second phase height H ₈₂ is not less than 0.42 times and not more than 0.56 times λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is 0.21 times or more and 0.28 times or less and satisfies the relationship that the first phase height H ₈₁ is higher than the second phase height H _82. Is formed as

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 80. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 80.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.525 as the material of the diffractive optical element 80. When a plastic resin having a refractive index N ₃ with respect to 783 nm of 1.503 is used, the grating pitch P _{8 is} 1.0, the width W _{81 is} 0.22, and the width W _{82 is} 0.06. In this case, the first phase height H ₈₁ = 1350 nm and the second phase height H ₈₂ = 920 nm are set.

That is, the first phase height H ₈₁ is 1.75 × λ ₁ / (N ₁ −1) and 0.87 × λ ₃ / (N ₃ −1), and the second phase height H _{81 82} is 1.19 × λ ₁ / (N ₁ −1) and 0.59 × λ ₃ / (N ₃ −1), and the first phase height H ₈₁ and the second phase height H The difference ΔH ₈ with respect to ₈₂ is 0.56 × λ ₁ / (N ₁ −1) and 0.28 × λ ₃ / (N ₃ −1), and the first phase height H ₈₁ is the second The phase height is higher than _H82 .

  The diffractive optical element 80 having such a diffractive portion 80a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction section 80a has a diffraction efficiency of 0. 3rd order light of 50.3% and a diffraction efficiency of ± 1st order light of 8.2% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 6.2, and the diffraction efficiency of the 0th order light is 55.2% and the diffraction efficiency of ± 1st order light is 7.9% for the third wavelength light beam. The light / first-order diffracted light intensity ratio is 7.0. The diffraction section 80a has a diffraction efficiency of 0th order light of 71.3% with respect to the second wavelength and a diffraction efficiency of ± 1st order light of 1.1%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 80 has a high diffraction efficiency of the 0th order light and the 0th order light with respect to the light beams of the first and third wavelengths that perform the 3-beam splitting for tracking error detection. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 90 is provided between the light source unit 3 and the beam splitter 5, and diffractive unit 90a that selectively splits the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is a surface on the emission side.

  The diffractive portion 90a of the diffractive optical element 90 diffracts the light beam of the first wavelength for the first optical disc into three beams, transmits the light beam of the second wavelength for the second optical disc, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams of the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 90, the diffractive unit 90a generates zero-order light and ± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. Further, the light beam having the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffracting unit 90a of the diffractive optical element 90 and is emitted to the beam splitter 5 side.

The first diffraction grating 90a includes a plurality of grating portions 91 each having a fine grating pattern as shown in FIG. Each grating part 91 is formed in a substantially stepped cross section, and has a first phase grating part 91a having a first phase height H ₉₁ and a predetermined width W ₉₁ with respect to the reference plane 91c, and the first phase grating part 91a. A second phase grating portion 91b is formed on both sides of the phase grating portion 91a in a stepped manner and has a second phase height H ₉₂ and a predetermined width W ₉₂ with respect to the reference plane 91c. Note that FIG. 12 in P ₉ is the grating pitch of each grating portion 91, that is, shows one pitch.

In the first phase grating portions 91a and 91b, the first and second phase heights H ₉₁ and H ₉₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₉₁ is not less than 1.32 times and not more than 1.93 times λ ₁ / (N ₁ -1) and not less than 0.65 times and not more than 0.96 times λ ₃ / (N ₃ -1); The second phase height H ₉₂ is not less than 0.01 times and not more than 0.59 times λ ₁ / (N ₁ −1), and is not less than 0.005 times λ ₃ / (N ₃ −1) and 0.29. The difference ΔH ₉ between the first phase height H ₉₁ and the second phase height H ₉₂ is 1.18 times or more and 1.36 times or less of λ ₁ / (N ₁ −1), And λ ₃ / (N ₃ −1) is 0.59 times to 0.68 times and satisfies the relationship that the first phase height H ₉₁ is higher than the second phase height H _92. Is formed as .

In the above relationship, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 90. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 90.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ with respect to 405 nm is 1.470 as the material of the diffractive optical element 90. When a glass glass material having a refractive index N ₃ with respect to 783 nm of 1.454 is used, the grating pitch P ₉ is set to 1.0, the width W ₉₁ is set to 0.188, and the width W _{92 is set to} 0.136. In this case, the first phase height H ₉₁ = 1180 nm and the second phase height H ₉₂ = 40 nm are set.

That is, the first phase height H ₉₁ is 1.37 × λ ₁ / (N ₁ −1) and 0.68 × λ ₃ / (N ₃ −1), and the second phase height H ₉₁ is ₉₂ is 0.05 × λ ₁ / (N ₁ −1) and 0.02 × λ ₃ / (N ₃ −1), and the first phase height H ₉₁ and the second phase height H The difference ΔH _{9 from 92} is 1.32 × λ ₁ / (N ₁ −1) and 0.66 × λ ₃ / (N ₃ −1), and the first phase height H ₉₁ is the second The phase height is higher than _H92 .

  The diffractive optical element 90 having such a diffractive portion 90a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction unit 90a has a diffraction efficiency of 0th order light of 50.0% and a diffraction efficiency of ± 1st order light of 12.1% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 4.1, and the diffraction efficiency of the 0th order light is 55.5% and the diffraction efficiency of ± 1st order light is 8.3% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 6.7. Further, the diffraction section 90a has a diffraction efficiency of 0th-order light with respect to the second wavelength of 80.1% and a diffraction efficiency of ± 1st-order light of 3.0%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 90 has a high 0th-order light diffraction efficiency for the first and third wavelength light beams that are split into three beams for tracking error detection, and at the same time, The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  In the optical pickup to which the present invention is applied, the composite optical element may be formed as follows. In the following description, the configuration other than the diffractive optical element is the same as that of the optical pickup 1 described above, and the common portions are denoted by the same reference numerals and the details thereof are omitted.

  The diffractive optical element 100 is provided between the light source unit 3 and the beam splitter 5 and selectively divides the light beams having the first to third wavelengths emitted from the light source unit 3 into three beams. Is a surface relief type grating-like diffractive optical element provided on the beam splitter 5 side which is the surface on the exit side.

  The diffractive portion 100a of the diffractive optical element 100 diffracts the light beam of the first wavelength for the first optical disk into three beams, transmits the light beam of the second wavelength for the second optical disk, and transmits the third light beam. A light beam having a third wavelength for an optical disk is diffracted into three beams.

  Specifically, when the light beams having the first or third wavelength emitted from the first and third light emitting units of the light source unit 3 are incident on the diffractive optical element 100, the diffractive unit 100a generates zero-order light and ± It is diffracted into three beams composed of primary light and emitted to the beam splitter 5 side. Further, the light beam of the second wavelength emitted from the second light emitting unit of the light source unit 3 is substantially transmitted through the diffractive unit 100a of the diffractive optical element 100 and is emitted to the beam splitter 5 side.

The first diffraction grating 100a is formed by repeatedly forming a plurality of grating portions 101 having a fine grating pattern as shown in FIG. Each grating part 101 is formed in a substantially stepped cross section, and has a first phase grating part 101a having a first phase height H ₁₀₁ and a predetermined width W ₁₀₁ with respect to the reference plane 101c. in the second phase the height _{H 102} against stepwise formed reference plane 101c on both sides of the phase grating portion 101a, and a second phase grating portions 101b having a predetermined width _{W 102.} Incidentally, in FIG. 13 _{P 10} is the grating pitch of each grating portion 101, that is, shows one pitch.

In the first phase grating portions 101a and 101b, the first and second phase heights H ₁₀₁ and H ₁₀₂ are not more than 2.00 times λ ₁ / (N ₁ −1), and the first phase height The height H ₁₀₁ is not less than 1.32 times and not more than 1.43 times λ ₁ / (N ₁ -1), and not less than 0.65 times and not more than 0.72 times λ ₃ / (N ₃ -1); second phase height _{H 102 is, λ 1 / (N 1 -1} ) of 1.25 times 1.36 times or less, and λ ₃ / _{(N 3} -1) of 0.62 times 0.68 The difference ΔH ₁₀ between the first phase height H ₁₀₁ and the second phase height H ₁₀₂ is 0.01 times or more and 0.11 times or less of λ ₁ / (N ₁ −1), and λ ₃ / _{(N 3} -1) or less 0.06 times 0.005 times more, satisfy the first phase the height _{H 101} is the second phase height _{H 102} becomes higher such relationship than It is formed in the Suyo.

In the above relation, λ ₁ is the first wavelength (nm), λ ₃ is the third wavelength (nm), and N ₁ is the first material of the diffractive optical element 100. the refractive index of the relative wavelength lambda _1, N ₃ is the refractive index for the third wavelength lambda ₃ of the material constituting the diffractive optical element 100.

For example, the first wavelength λ ₁ is 405 nm, the second wavelength λ ₂ is 658 nm, the third wavelength λ ₃ is 783 nm, and the refractive index N ₁ for 405 nm is 1.525 as the material of the diffractive optical element 100. When a plastic resin having a refractive index N ₃ with respect to 783 nm is 1.503, the grating pitch P ₁₀ = 1.0, the width W ₁₀₁ = 0.124, and the width W ₁₀₂ = 0.348. In this case, the first phase height H ₁₀₁ = 1090 nm and the second phase height H ₁₀₂ = 1030 nm.

That is, the first phase height H ₁₀₁ is 1.41 × λ ₁ / (N ₁ −1) and 0.70 × λ ₃ / (N ₃ −1), and the second phase height H _{101 102} is 1.34 × λ ₁ / (N ₁ −1) and 0.66 × λ ₃ / (N ₃ −1), and the first phase height H ₁₀₁ and the second phase height H The difference ΔH ₁₀ with respect to ₁₀₂ is 0.08 × λ ₁ / (N ₁ −1) and 0.04 × λ ₃ / (N ₃ −1), and the first phase height H ₁₀₁ is the second The phase height is higher than _H102 .

  The diffractive optical element 100 having such a diffractive portion 100a diffracts the light beams of the first and third wavelengths into the main beam and the two sub beams at an appropriate 0th-order light / first-order light diffracted light intensity ratio. A light beam having a wavelength of 2 is transmitted with an appropriate transmittance. That is, the diffraction section 100a has a diffraction efficiency of 0th order light of 52.0% and a diffraction efficiency of ± 1st order light of 10.0% with respect to the light beam of the first wavelength. The diffracted light intensity ratio is 5.2, and the diffraction efficiency of the 0th order light is 55.4% and the diffraction efficiency of ± 1st order light is 7.9% with respect to the light beam of the third wavelength. The light / first-order diffracted light intensity ratio is 7.0. Further, the diffraction section 100a has a diffraction efficiency of 0-order light with respect to the second wavelength of 78.7% and a diffraction efficiency of ± 1st-order light of 3.1%, so that a sufficient transmittance can be obtained.

  As described above, the diffractive optical element 100 has high zero-order light diffraction efficiency for the first and third wavelength light beams that are divided into three beams for tracking error detection, and at the same time, the zero-order light. The light intensity ratio with ± 1st order light can be set within an appropriate range, and the light beam with the second wavelength that is not divided into three beams for tracking error detection is transmitted with an appropriate transmittance. High diffraction efficiency of 0th order light.

  Even with an optical pickup provided with the diffractive optical elements 20, 30, 40, 50, 60, 70, 80, 90, and 100 as described above, recording and reproduction are performed on a plurality of types of optical disks using light beams of three different wavelengths. When the tracking error signal is detected when performing diffracting optical elements 20, 30, 40, 50, 60, 70, 80, 90, 100, the diffractive portions 20a, 30a, 40a, 50a, 60a, 70a, 80a, 90a and 100a can generate three beams with the optimal diffraction efficiency for the light beams of the first and third wavelengths that are split into three beams, and the light beams of the wavelengths that are not split into three beams. Since the light can be transmitted with an appropriate transmittance, the laser utilization efficiency of the light beams of the respective wavelengths emitted from the first to third light emitting units of the light source unit 3 is improved. The light beam of each wavelength can be performed accurately tracking error detection using.

  In the optical pickup to which the present invention is applied, the wavelength of the laser light emitted from the three-wavelength semiconductor laser element can be changed according to the various optical disks 8, and is limited to the above-described lasers with the wavelength of 405 nm, the wavelength of 660 nm, and the wavelength of 785 nm. Is not to be done.

1 is an optical path diagram showing an optical system of an optical pickup to which the present invention is applied. It is a side view which shows the diffraction part of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a top view which shows the spot of the main beam and sub beam with which the signal recording surface of the optical disk was irradiated, (a) is a top view in the case of a differential push pull (DPP) system, (b) is a 3 spot system. It is a top view in the case of. It is a top view which shows the photodetector which comprises the optical pick-up to which this invention was applied. It is a side view which shows the diffraction part of the other example of the diffractive optical element which comprises the optical pick-up to which this invention was applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied. It is a side view which shows the diffraction part of the further another example of the diffractive optical element which comprises the optical pick-up to which this invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical pick-up, 3 Light source part, 4 Diffractive optical element, 4a Diffractive part, 5 Beam splitter, 6 Collimator lens, 7 Objective lens, 8 Optical disk, 9 Plate optical element, 10 Photo detector, 11 Grating part, 11a 1st 11b 2nd phase grating part, 14 1st light-receiving surface, 15 2nd light-receiving surface, 16 3rd light-receiving surface, 17th 4th light-receiving surface, 18 5th light-receiving surface, 19 6th Light receiving surface

Claims (14)

A first light emitting unit that emits a light beam of a first wavelength;
A second light emitting unit for emitting a light beam of a second wavelength;
A third light emitting unit that emits a light beam of a third wavelength;
A first phase grating portion having a first phase height with respect to a reference plane; and a second phase grating having a second phase height with respect to the reference plane on both sides of the first phase grating portion. The first and third light beams having a two-stage phase height and being incident with the optical axes of the light beams emitted from the first to third light emitting portions being coincident with each other. A diffractive optical element having a diffractive portion for dividing the beam into three beams;
An objective lens for condensing the light beam emitted from the first to third light emitting units on the signal recording surface of the optical disc;
A photodetector for detecting a return light beam reflected by the optical disc,
When the first wavelength is λ ₁ and the refractive index of the diffractive optical element with respect to the first wavelength λ ₁ is N ₁ , the first and second phase heights are both 2 × λ ₁ / (N ₁ -1) An optical pickup that is less than or equal to.   2. The light according to claim 1, wherein the diffractive optical element divides the light beams having the first and third wavelengths into three beams so that a diffracted light intensity ratio of the zero-order light to the first-order light is 3 to 10. 3. pick up.   The optical pickup according to claim 1, further comprising a light source unit having the first to third light emitting units. The first wavelength is around 405 nm,
The second wavelength is around 660 nm,
The optical pickup according to claim 1, wherein the third wavelength is around 785 nm. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 0.01 times or more and 0.67 times or less of λ ₁ / (N ₁ -1), and 0.005 times or more and 0.34 times of λ ₃ / (N ₃ -1). And
The second phase height is 1.34 times or more and 2.00 times or less of λ ₁ / (N ₁ -1) and 0.66 times or more and 1.00 times of λ ₃ / (N ₃ -1). And
The difference between the first phase height and the second phase height is 1.18 times or more and 1.36 times or less of λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.59 times or more and 0.68 times or less,
5. The optical pickup according to claim 4, wherein the second phase height is higher than the first phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 0.99 times or more and 1.36 times or less of λ ₁ / (N ₁ -1), and 0.49 times or more and 0.68 times of λ ₃ / (N ₃ -1). And
The second phase height is 1.55 times or more and 2.00 times or less of λ ₁ / (N ₁ -1) and 0.77 times or more and 1.00 times of λ ₃ / (N ₃ -1). And
The difference between the first phase height and the second phase height is not less than 0.44 times and not more than 0.67 times λ ₁ / (N ₁ −1), and λ ₃ / (N ₃ −1). 0.21 times or more and 0.34 times or less,
5. The optical pickup according to claim 4, wherein the second phase height is higher than the first phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 0.88 times or more and 1.20 times or less of λ ₁ / (N ₁ -1) and 0.43 times or more and 0.60 times of λ ₃ / (N ₃ -1). And
The second phase height is 1.14 to 1.63 times λ ₁ / (N ₁ −1) and 0.57 to 0.82 times λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is not less than 0.23 times and not more than 0.42 times λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.11 times or more and 0.21 times or less,
5. The optical pickup according to claim 4, wherein the second phase height is higher than the first phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 0.63 times or more and 1.10 times or less of λ ₁ / (N ₁ -1) and 0.31 times or more and 0.55 times of λ ₃ / (N ₃ -1). And
The second phase height is 0.49 times or more and 0.85 times or less of λ ₁ / (N ₁ −1), and 0.24 times or more and 0.42 times of λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is not less than 0.03 times and not more than 0.32 times λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.01 times or more and 0.16 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 0.83 times or more and 1.13 times or less of λ ₁ / (N ₁ -1) and 0.41 times or more and 0.57 times of λ ₃ / (N ₃ -1). And
The second phase height is 0.58 times or more and 0.86 times or less of λ ₁ / (N ₁ −1), and 0.28 times or more and 0.43 times of λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is not less than 0.22 times and not more than 0.42 times λ ₁ / (N ₁ -1) and λ ₃ / (N ₃ -1). 0.10 times or more and 0.21 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is not less than 0.63 times and not more than 0.69 times λ ₁ / (N ₁ −1), and not less than 0.31 times and not less than 0.35 times λ ₃ / (N ₃ −1). And
The second phase height is 0.03 to 0.20 times λ ₁ / (N ₁ −1) and 0.01 to 0.10 times λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is 0.49 times or more and 0.63 times or less of λ ₁ / (N ₁ −1), and λ ₃ / (N ₃ −1). 0.24 times or more and 0.31 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 1.26 times to 1.36 times λ ₁ / (N ₁ -1) and 0.63 times to 0.68 times λ ₃ / (N ₃ -1). And
The second phase height is 1.33 times or more and 1.53 times or less of λ ₁ / (N ₁ −1) and 0.66 times or more and 0.76 times of λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is 0.01 times or more and 0.24 times or less of λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.005 times or more and 0.12 times or less,
5. The optical pickup according to claim 4, wherein the second phase height is higher than the first phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 1.65 times or more and 1.75 times or less of λ ₁ / (N ₁ -1) and 0.82 times or more and 0.87 times of λ ₃ / (N ₃ -1). And
The second phase height is 1.18 times or more and 1.25 times or less of λ ₁ / (N ₁ -1) and 0.59 times or more and 0.62 times of λ ₃ / (N ₃ -1). And
The difference between the first phase height and the second phase height is not less than 0.42 times and not more than 0.56 times λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.21 times or more and 0.28 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 1.32 times or more and 1.93 times or less of λ ₁ / (N ₁ -1) and 0.65 or more and 0.96 times of λ ₃ / (N ₃ -1). And
The second phase height is 0.01 times or more and 0.59 times or less of λ ₁ / (N ₁ -1), and 0.005 times or more and 0.29 times of λ ₃ / (N ₃ -1). And
The difference between the first phase height and the second phase height is 1.18 times or more and 1.36 times or less of λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.59 times or more and 0.68 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height. When the third wavelength is λ ₃ and the refractive index of the diffractive optical element with respect to the third wavelength λ ₃ is N ₃ ,
The first phase height is 1.32 times or more and 1.43 times or less of λ ₁ / (N ₁ −1) and 0.65 times or more and 0.72 times of λ ₃ / (N ₃ −1). And
The second phase height is 1.25 to 1.36 times λ ₁ / (N ₁ −1) and 0.62 to 0.68 times λ ₃ / (N ₃ −1). And
The difference between the first phase height and the second phase height is 0.01 times or more and 0.11 times or less of λ ₁ / (N ₁ −1) and λ ₃ / (N ₃ −1). 0.005 times or more and 0.06 times or less,
The optical pickup according to claim 4, wherein the first phase height is higher than the second phase height.

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