JP2008159140A - Diffraction element and manufacturing method of diffraction element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a diffraction element having a fine and accurate diffraction pattern. <P>SOLUTION: When a diffraction pattern layer 20D wherein the diffraction pattern PTc in a step shape of a plurality of steps is formed is provided by pressurizing a metal mold to a photosetting resin 100A applied on one surface of a base member 20C and irradiating the photosetting resin with UV to cure the resin, each diffraction pattern layer 20D is formed into a plurality of layers for every step of a part of the diffraction patterns. Thereby, the depth of the shape of the metal mold is reduced to enhance accuracy thereof and the diffraction element 20 having satisfactory shape accuracy and high diffraction efficiency is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diffractive element and a method for manufacturing the diffractive element, and is suitable for application to, for example, a diffractive element used in an optical pickup.

  Conventionally, in an optical pickup of an optical disc apparatus, a diffraction element is used for the purpose of correcting an aberration of a light beam. A diffraction element forms a fine groove-shaped diffraction grating on the surface of a transparent plate-shaped element substrate, and diffracts a light beam by an optical path difference when passing through the peaks and valleys of the diffraction grating (for example, , See Patent Document 1).

Here, the diffraction efficiency of the diffractive element changes according to the groove depth of the diffraction pattern forming the diffraction grating and the wavelength of the light beam, and the diffraction angle changes according to the period of the diffraction pattern (or the groove width). To do.
JP 2005-339762 A

  As a method for manufacturing such a diffraction element, for example, an ultraviolet curable resin (hereinafter referred to as UV (Ultra Violet ray) curable resin) is applied to a base member made of an injection molded product of a transparent resin, and then the applied UV is applied. By irradiating ultraviolet light while pressing a mold having a mold shape with an inverted diffraction pattern against the cured resin, the UV cured resin is cured in a state where the mold shape of the mold is transferred to the base member. There is a so-called UV replica method for forming a diffraction pattern using a UV curable resin. Such a UV replica method has an advantage that a precise diffraction pattern can be formed with less deformation compared to a conventional diffraction element by injection molding.

  As a technique for producing a mold used in the UV replica method, there are a machining method and a wafer process.

  The machining method is to create a die shape by cutting a mold base material, but in a diffraction pattern with a small pitch and a deep depth (that is, a large aspect ratio) (for example, a pitch of 10 [μm] or less) , Depth of 10 [μm] or more), the tool for processing the mold becomes smaller and the dimensional accuracy and rigidity are lowered, so that it is impossible to create a precise mold shape. There is a problem that a diffraction pattern cannot be formed.

  On the other hand, the wafer process creates a mold shape by etching the base material, and can create a more precise mold shape than the above-described machining method. FIG. 1 shows a procedure for producing a mold using a wafer process. First, as shown in FIG. 1A, a resist 52 is applied to the surface of a base material 51 made of, for example, silicon.

  Next, as shown in FIG. 1B, after a mask 53 having a mask pattern corresponding to the mold shape is positioned on the resist 52 and exposed with light of a predetermined wavelength, the resist 52 is developed, As shown in FIG. 1C, an exposure pattern corresponding to the mask pattern is formed on the surface of the resist 52.

  Then, the substrate 51 is subjected to, for example, reactive ion etching (hereinafter also referred to as RIE) processing and resist cleaning processing through the resist 52 on which the exposure pattern is formed, so that FIG. As shown in FIG. 2, a mold shape as a mold corresponding to the mask pattern of the mask 53 is formed on the surface of the base material 51.

  However, although such a wafer process can perform high-precision processing of, for example, 100 [nm] or less in the pitch direction of the pattern to be processed, there is a problem that processing accuracy decreases as the processing depth increases. A mold shape having a large ratio cannot be produced with high accuracy, and a mold produced by the wafer process has a problem that a diffraction pattern having a large aspect ratio cannot be formed with high accuracy.

  The present invention has been made in consideration of the above points, and intends to propose a diffraction element having a fine and accurate diffraction pattern and a method for manufacturing the same.

  In order to solve this problem, in the diffractive element of the present invention, a plurality of steps are formed on the surface opposite to the surface in contact with the base member by pressing the mold against the photocurable resin applied to one surface of the base member and curing it. A diffraction pattern layer formed by forming a diffraction pattern having a stepped shape is provided, and the diffraction pattern layer is divided into a plurality of layers for each step of the diffraction pattern.

  As a result, the mold for forming the diffraction pattern layer can be divided into a plurality of layers to reduce the mold depth of each mold. The diffraction element which has can be obtained.

  Further, in the method for manufacturing a diffraction element according to the present invention, a method for manufacturing a diffraction element in which a diffraction pattern layer having a plurality of stepped diffraction patterns formed of a photocurable resin is provided on one surface of a base member. In addition, by pressing and curing a mold having a mold shape obtained by inverting the shape of some steps including the lowest step of the diffraction pattern against the photocurable resin applied to one surface of the base member, the diffraction pattern The step of forming a part of the layer, and the photocurable resin applied to the surface of the part of the formed diffraction pattern layer, all or some of the unformed stages of the diffraction pattern A step of forming all or a part of the remaining layers in the diffraction pattern layer by pressing and curing a mold having a mold shape that is inverted in shape.

  As a result, the mold for forming the diffraction pattern layer can be divided into a plurality of layers to reduce the mold depth of each mold. The diffraction element which has can be obtained.

  According to the present invention, a diffraction pattern consisting of a plurality of steps is formed on the opposite surface of the surface in contact with the base member by pressing and curing the mold to the photo-curable resin applied to one surface of the base member. When the formed diffraction pattern layer is provided, the diffraction pattern layer is divided into a plurality of layers for each part of the diffraction pattern, thereby providing a mold for forming the diffraction pattern layer. The mold depth of each mold can be reduced by dividing into multiple layers, each mold can be created with high accuracy, and a diffraction element having a fine and accurate diffraction pattern and a method for manufacturing the same can be realized. it can.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Optical Disc Device (1-1) Overall Configuration of Optical Disc Device In FIG. 2, reference numeral 1 denotes an optical disc device using a diffraction element according to the present invention, which is a CD (Compact Disc) system and a DVD (Digital Versatile Disc) system. Alternatively, the optical disc 100 can be played back by any one of three methods such as a BD (Blu-ray Disc, registered trademark) method.

  The optical disc device 1 is configured to be controlled in an integrated manner by the control unit 2. When a reproduction instruction or the like from an external device (not shown) is received in a state where the optical disc 100 is loaded, a drive unit is received from the control unit 2. 3 and the signal processing unit 4 are controlled to read information recorded on the optical disc 100.

  In practice, the drive unit 3 rotates the optical disc 100 at a desired rotational speed by the spindle motor 5 based on the control of the control unit 2, and the sled motor 6 increases the optical pickup 7 in the tracking direction which is the radial direction of the optical disc 100. Further, the biaxial actuator 8 finely moves the objective lens unit 9 in two directions, ie, a focus direction and a tracking direction, which are directions in which the objective lens unit 9 approaches or separates from the optical disc 100.

  In parallel with this, the signal processing unit 4 irradiates the desired track of the optical disc 100 with a predetermined light beam from the objective lens unit 9 by the optical pickup 7, and generates a reproduction signal based on the detection result of the reflected light. The reproduction signal is sent to an external device (not shown) via the control unit 2.

  The optical pickup 7 is a so-called three-wavelength compatible type, and light having a wavelength of about 780 [nm] from the objective lens unit 9 to the optical disk 100 of the CD system (hereinafter referred to as the CD system disk 100c). The optical disc 100 is irradiated with a beam, and an optical beam 100 having a wavelength of about 650 [nm] is irradiated onto an optical disc 100 made of DVD (hereinafter referred to as a DVD disc 100d). This is called a BD type disc 100b) and is irradiated with a light beam having a wavelength of about 405 [nm].

  As described above, the optical disc apparatus 1 can reproduce the optical disc 100 by irradiating the optical disc 100 of the CD format, DVD format, or BD format with a light beam suitable for each format. .

(1-2) Configuration of Optical Pickup As shown in FIG. 3, the optical pickup 7 uses a light beam having a wavelength of about 780 [nm] corresponding to the CD system (hereinafter referred to as CD light) as a light beam light source. A laser diode 11 capable of emitting a light beam having a wavelength of about 650 [nm] corresponding to the DVD system (hereinafter referred to as a DVD light beam Ld) and a wavelength of about BD. And a laser diode 12 capable of emitting a light beam having a wavelength of 405 [nm] (hereinafter referred to as a BD light beam Lb).

  The coupling lens 13 converts the optical magnification of the light beam emitted from the laser diode 11.

  The beam splitter 14 reflects or transmits the light beam according to the wavelength at the reflection / transmission surface 14A. The light beam for CD Lc having a wavelength of about 780 [nm] is reflected on the reflection / transmission surface 14A. The DVD light beam Ld having a wavelength of about 650 [nm] is reflected, and the BD light beam Lb having a wavelength of about 405 [nm] is transmitted.

  The polarization beam splitter 15 reflects or transmits the light beam according to the polarization direction on the polarization plane 15A, transmits the light beam incident from the beam splitter 14 side, and adjusts the polarization direction. Thus, the light beam incident from the collimator lens 16 side is reflected.

  The collimator lens 16 converts the light beam incident from the polarization beam splitter 15 and made of divergent light into parallel light, and converts the light beam made incident from the rising mirror 17 and made of parallel light into convergent light. .

  The rising mirror 17 reflects the horizontal light beam incident from the collimator lens 16 and raises it in the vertical direction, that is, the direction in which the light beam is incident substantially perpendicularly to the optical disc 100. The vertically incident light beam is reflected and laid in the horizontal direction.

  The ¼ wavelength plate 18 converts the light beam incident from the rising mirror 17 from linearly polarized light to circularly polarized light by delaying the phase of a part of the component in the light beam by ¼ wavelength, or an objective lens. The light beam incident from the unit 9 is converted from circularly polarized light to linearly polarized light.

  As shown in the perspective view of FIG. 4, the objective lens unit 9 has a flat disk-shaped diffraction element 20 attached to the lower part of a substantially cylindrical lens barrel portion 19 (partially cut surface is shown in FIG. 4). In addition, a spindle-shaped part having a slightly smaller diameter than that of the disk is integrally formed on the lower surface of a flat disk-like part having the same size as that of the diffraction element 20 from the upper part to the center part of the lens barrel part 19. The objective lens 21 having the shape as described above is attached.

  The objective lens unit 9 converts the light beam incident from the quarter-wave plate 18 and made of parallel light into convergent light by the diffraction element 20 and the objective lens 21, and focuses it on the signal recording surface of the optical disc 100. Has been made.

  The optical pickup 7 converts the light beam reflected and diverged from the signal recording surface of the optical disc 100 into parallel light by the objective lens 21 and the diffraction element 20 of the objective lens unit 9, and is converted by the quarter wavelength plate 18. The light is converted from circularly polarized light to linearly polarized light, is laid down in the horizontal direction by the raising mirror 17, that is, in the direction in which the polarizing beam splitter 15 is provided, and is converted from parallel light to convergent light by the collimator lens 16, and then to the polarizing beam splitter 15. Make it incident.

  In this case, the polarization beam splitter 15 reflects the light beam on the polarization plane 15A in accordance with the polarization direction of the light beam and makes it incident on the conversion lens 22.

  The conversion lens 22 converts the optical magnification of the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb. The optical axis synthesizing element 23 matches the optical axes of the CD light beam Lc and DVD light beam Ld emitted from the laser diode 11 with the optical axis of the BD light beam Lb emitted from the laser diode 12. Has been made.

  A plurality of detection regions each having a predetermined shape are formed at predetermined positions on the upper surface of the photodetector 24 (that is, the surface irradiated with the light beam that has passed through the conversion lens 22 and the optical axis combining element 23). A plurality of detection signals are generated by detecting and photoelectrically converting the light amounts of the emitted light beams, and supplying the detection signals to the signal processing unit 4 (FIG. 2).

  In response to this, the signal processing unit 4 generates a reproduction RF signal by performing predetermined arithmetic processing using the detection signal from the photodetector 24 (FIG. 3), and performs predetermined decoding based on the reproduction RF signal. A reproduction signal is generated through processing, demodulation processing, and the like.

  Further, the signal processing unit 4 performs predetermined arithmetic processing using the detection signal from the photodetector 24 to generate a drive control signal such as a tracking error signal and a focus error signal, and sends these signals to the control unit 2. It is made to supply. In response to this, the control unit 2 performs tracking control, focus control, and the like via the drive unit 3 and can adjust the irradiation state of the light beam to the optical disc 100 to normally generate a reproduction signal.

(1-2-1) In the case of a CD-type disc In practice, when the control unit 2 (FIG. 2) recognizes that the optical disc 100 is a CD-type disc 100c by a predetermined disc type determination method, the optical pickup 7 ( A CD light beam Lc made of divergent light is emitted from the light emitting point 11 A of the laser diode 11 in FIG. 3) and is incident on the beam splitter 14 through the coupling lens 13.

  The optical pickup 7 reflects the CD light beam Lc at the reflection / transmission surface 14 A by the beam splitter 14, transmits the polarization beam splitter 15, converts the divergent light into parallel light by the collimator lens 16, and After rising from the horizontal direction to the vertical direction and converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 18, the CD light beam Lc is incident on the objective lens unit 9.

  The objective lens unit 9 converts the CD light beam Lc incident from the quarter-wave plate 18 into convergent light by the diffraction element 20 and the objective lens 21, and focuses this on the signal recording surface of the CD disc 100c. .

  The objective lens unit 9 converts the CD light beam Lc reflected on the signal recording surface of the CD disc 100c into divergent light into parallel light by the objective lens 21 and the diffractive element 20, and the quarter-wave plate 18 is converted. To enter.

  Thereafter, the optical pickup 7 converts the CD light beam Lc incident on the quarter-wave plate 18 from circularly polarized light to linearly polarized light, lays it horizontally by the rising mirror 18, and converges light from parallel light by the collimator lens 16. Then, the light is reflected on the polarization plane 15A by the polarization beam splitter 15, and sequentially passes through the conversion lens 22 and the optical axis synthesizing element 23 to irradiate the photodetector 24.

  The photodetector 24 detects the light amount of the irradiated CD light beam Lc by a plurality of detection regions, generates a plurality of detection signals, and supplies the detection signals to the signal processing unit 4 (FIG. 2).

  In response to this, the signal processing unit 4 generates a reproduction RF signal based on a plurality of detection signals, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal. Has been made.

(1-2-2) In the case of a DVD type disc When the controller 2 (FIG. 2) recognizes that the optical disc 100 is a DVD type disc 100d by a predetermined disc type determination method, the optical pickup 7 (FIG. 3) The DVD light beam Ld made of divergent light is emitted from the light emitting point 11B of the laser diode 11 and is incident on the beam splitter 14 via the coupling lens 13.

  Thereafter, as in the case of the CD system disc 100c, the optical pickup 7 converts the DVD light beam Ld into the coupling lens 13, the beam splitter 14, the polarization beam splitter 15, the collimator lens 16, the rising mirror 17 and the quarter wavelength plate. Then, the light beam Ld for DVD is converted into convergent light by the diffraction element 20 and the objective lens 21 in the objective lens unit 9, and is focused on the signal recording surface of the DVD type disc 100d.

  Similarly to the case of the CD disc 100c, the objective lens unit 9 converts the DVD light beam Ld, which has been reflected and diverged from the signal recording surface of the DVD disc 100d, into parallel light by the objective lens 21 and the diffraction element 20. After the conversion, the ¼ wavelength plate 18, the rising mirror 17, the collimator lens 16, the polarization beam splitter 15, the conversion lens 22, and the optical axis synthesizing element 23 are passed or reflected in this order to irradiate the photodetector 24.

  As in the case of the CD system disc 100c, the photodetector 24 generates a plurality of detection signals by detecting the amount of light of the irradiated DVD light beam Ld using a plurality of detection areas, and generates these signals as a signal processing unit 4 (FIG. 2). ).

  In response to this, the signal processing unit 4 generates a reproduction RF signal, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal.

(1-2-3) In the case of a BD disc When the control unit 2 (FIG. 2) recognizes that the optical disc 100 is a BD disc 100b by a predetermined disc type determination method, the optical pickup 7 (FIG. 3) A BD light beam Lb made of divergent light is emitted from the light emitting point 12 A of the laser diode 12 and is incident on the beam splitter 14.

  In this case, the beam splitter 14 transmits the BD light beam Lb through the reflection / transmission surface 13 </ b> A and makes it incident on the polarization beam splitter 15.

  Thereafter, the optical pickup 7 passes or reflects the BD light beam Lb in the order of the polarizing beam splitter 15, the collimator lens 16, the rising mirror 17 and the quarter wavelength plate 18 in the same manner as in the case of the CD disc 100c, and the objective lens. In the unit 9, the BD light beam Lb is converted into convergent light by the objective lens 21, and this is focused on the signal recording surface of the BD disc 100b.

  Incidentally, the diffractive element 20 of the objective lens unit 9 transmits the BD light beam Lb as it is without being diffracted (details will be described later).

  Similarly to the case of the CD disc 100c, the objective lens unit 9 converts the BD light beam Lb, which is reflected from the signal recording surface of the BD disc 100b and becomes divergent light, into parallel light by the objective lens 21. The quarter-wave plate 18, the rising mirror 17, the collimator lens 16, the polarization beam splitter 15, the conversion lens 22, and the optical axis synthesizing element 23 are passed or reflected in this order, and are irradiated to the photodetector 24.

  As in the case of the CD system disc 100c, the photodetector 24 generates a plurality of detection signals by detecting the amount of light of the irradiated BD light beam Lb by using a plurality of detection areas, and generates these signals as a signal processing unit 4 (FIG. 2). ).

  In response to this, the signal processing unit 4 generates a reproduction RF signal, generates a reproduction signal, and generates a drive control signal such as a tracking error signal and a focus error signal.

  As described above, the optical pickup 7 has a CD light beam Lc, a DVD light beam Ld, or a DVD light beam Ld by the objective lens unit 9 regardless of whether the optical disk 100 is a CD disk 100c, a DVD disk 100d, or a BD disk 100b. The BD light beam Lb can be focused on the signal recording surface of the optical disc 100, and the reflected light can be detected by the photodetector 24.

(1-3) Configuration of Objective Lens Unit Next, FIG. 5 shows an enlarged cross-sectional view of the objective lens unit 9 and the CD disc 100c, DVD disc 100d and BD disc 100b. Incidentally, although the biaxial actuator 8 (FIG. 2) is attached to the objective lens unit 9, it is omitted in FIG.

  In general, in the CD system, DVD system, and BD system, from the viewpoint of compatibility and the like, the wavelength of the light beam for reading information, the numerical aperture for condensing the light beam, and signal recording from the lower surface of each optical disc 100 The thickness of the portion up to the surface (so-called cover layer) is defined by the standards.

  Specifically, in the CD system, the wavelength is specified to be about 780 [nm], the numerical aperture is about 0.45, and the thickness of the cover layer is 1.2 [mm]. In the DVD system, the wavelength is about 650 [nm]. nm], a numerical aperture of about 0.65, and a cover layer thickness of 0.6 [mm]. In the BD method, the wavelength is about 405 [nm], the numerical aperture is about 0.85, and the cover The thickness of the layer is defined as 0.1 [mm].

  In the objective lens unit 9, due to the characteristics of the objective lens 21, the focal lengths when the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb are respectively irradiated from the objective lens 21 are different. .

  For this reason, in the optical disk apparatus 1, by actually adjusting the height of the objective lens unit 9 (that is, the distance from the optical disk 100) via the biaxial actuator 8 (FIG. 2) while the height of the optical disk 100 is fixed. Each light beam is focused on the signal recording surface of each optical disk.

  Incidentally, in FIG. 5, for the convenience of explanation, the objective lens unit 9 is fixed and the height of the optical disc 100 is changed. As a result, in FIG. 5, the height of the lower surface of each optical disk is different. In FIG. 4, only the cover layer is shown for the CD disc 100c, DVD disc 100d, and BD disc 100b.

  By the way, the objective lens 21 has priority over the CD light beam Lc and the DVD light beam Ld from the viewpoint of the relative intensity of the BD light beam Lb and the numerical aperture defined by the BD method. The design is optimized for the light beam Lb.

  For this reason, the objective lens 21 of the objective lens unit 9 converts the BD light beam Lb into convergent light when the BD light beam Lb is incident as parallel light from the lower side of the objective lens 21, and converts the BD light beam Lb into convergent light. It is possible to focus on the signal recording surface of 100b.

  However, since the objective lens 21 is optimized for the BD light beam Lb, if the CD light beam Lc or the DVD light beam Ld is incident as parallel light from the lower side of the objective lens 21, it is converted into convergent light. Although it can be converted, aberration is generated and the signal recording layer of the optical disc 100 cannot be correctly focused.

  Therefore, the objective lens unit 9 selectively diffracts only the CD light beam Lc or the DVD light beam Ld by the diffraction element 20 and makes it enter the objective lens 21 as non-parallel light, and the BD light beam Lb is converted into parallel light. The light is incident on the objective lens 21 as it is.

  Specifically, the diffraction element 20 has a CD diffraction grating DGc formed on the upper layer portion 20A, which is a hologram that diffracts the CD light beam Lc and does not diffract the DVD light beam Ld and the BD light beam Lb. As shown in FIG. 5, the CD light beam Lc is diffracted slightly outward by the CD diffraction grating DGc.

  That is, the upper layer portion 20A of the diffraction element 20 can transmit the DVD light beam Ld and the BD light beam Lb as they are, and can selectively diffract only the CD light beam Lc, in other words, the CD light beam. It functions as a lens that corrects only the aberration of Lc.

  In response to this, the objective lens 21 refracts the CD light beam Lc incident from the diffraction element 20 on the lower surface and the upper surface, respectively, and converts it into convergent light, as shown in FIG. As a result, the objective lens unit 9 can correct the aberration of the CD light beam Lc, and can focus the CD light beam Lc irradiated from the objective lens 21 on the signal recording surface of the CD system disc 100c. .

  In the diffraction element 20, a DVD diffraction grating DGd is formed in the lower layer portion 20B, which is a hologram that diffracts the DVD light beam Ld and does not diffract the CD light beam Lc and the BD light beam Lb. As shown in FIG. 5, the DVD light beam Ld is slightly diffracted outward by the DVD diffraction grating DGd.

  That is, the lower layer portion 20B of the diffraction element 20 can transmit the CD light beam Lc and the BD light beam Lb as they are, and can selectively diffract only the DVD light beam Ld, in other words, the DVD light beam. It functions as a lens that corrects only the Ld aberration.

  In response to this, the objective lens 21 refracts the DVD light beam Ld incident from the diffraction element 20 on the lower surface and the upper surface, respectively, and converts it into convergent light, as shown in FIG. As a result, the objective lens unit 9 can correct the aberration of the DVD light beam Ld, and can focus the DVD light beam Ld irradiated from the objective lens 21 on the signal recording surface of the DVD disc 100d. .

  In this way, the objective lens unit 9 corrects the aberration by diffracting only the CD light beam Lc by the upper layer portion 20A of the diffractive element 20, and diffracts only the DVD light beam Ld by the lower layer portion 20B of the diffractive element 20. By correcting the aberration, the CD light beam Lc, the DVD light beam Ld, and the BD light beam Lb irradiated from the objective lens 21 optimized for the BD light beam Lb are converted into the CD disk 100c and the DVD disk. Each of the signal recording surfaces of the disc 100d and the BD disc 100b can be focused.

(1-4) Configuration of Diffraction Element As shown in FIG. 6A, the diffraction element 20 is configured around a base layer 20C formed in a generally flat disk shape, as described above. A CD diffraction grating DGc is formed in the upper layer portion 20A, and a DVD diffraction grating DGd is formed in the lower layer portion 20B.

  The base layer 20C is a disk having a flat upper and lower surface, and is formed by injection molding a transparent synthetic resin having a predetermined refractive index.

  On the other hand, as shown in FIG. 6B, the upper layer portion 20A has a CD diffraction pattern layer 20D joined to the upper surface 20Ca of the base layer 20C formed in a planar shape, and a cover layer on the upper side. 20E is joined and formed.

  The CD diffraction pattern layer 20D is made of a transparent resin having a refractive index substantially equal to that of the base layer 20C, and stepwise CD diffraction patterns PTc are periodically formed on the upper surface side. This CD diffraction pattern PTc is formed in two steps (three steps), and the depth per step should be the refractive index dispersion and transmission / diffraction of the CD diffraction pattern layer 20D and the cover layer 20E. Determined based on wavelength and order. The repetition period (that is, pitch) of the CD diffraction pattern PTc is determined based on the phase of the wavelength to be corrected by the hologram.

  Actually, the total depth of the CD diffraction pattern PTc is 12 [μm], and the pitch of the CD diffraction pattern PTc is 10 [μm]. Further, as shown in FIG. 4, the CD diffraction pattern PTc is concentrically formed in a range from the center to about half of the outer diameter on the upper surface of the diffraction element 20.

  The cover layer 20E is made of a material having a refractive index different from that of the CD diffraction pattern layer 20D, and its lower surface is formed so as to be joined to the CD diffraction pattern PTc without a gap, and its upper surface is planar. It is formed in a shape.

  As described above, the upper layer portion 20A of the diffraction element 20 has a refractive index substantially equal to that of the base layer 20C in which the stepped CD diffraction pattern PTc is periodically formed on the upper surface 20Ca of the base layer 20C. The pattern layer 20D is bonded, and the cover layer 20E having a refractive index different from that of the diffraction pattern layer 20D is bonded to the upper side of the pattern layer 20D, thereby diffracting or transmitting the light beam according to the wavelength. It functions as a CD diffraction grating DGc that diffracts only the CD light beam Lc as the light beam of one wavelength.

  On the other hand, as shown in FIG. 6C, the lower layer portion 20B is a DVD diffraction pattern layer in which a DVD diffraction grating DGd is formed on the lower surface 20Cb of the planar base layer 20C. 20F is joined and formed.

  The DVD diffraction pattern layer 20F is also made of a transparent resin having a refractive index substantially equal to that of the base layer 20C, and stepwise DVD diffraction patterns PTd are periodically formed on the lower surface side. The lower surface of the diffraction pattern layer 20F for DVD is directly covered with air because it is not covered with other substances.

  The DVD diffraction pattern PTd is formed in four steps (five steps), the total depth is 6 [μm], and the pitch is 170 [μm]. Further, as shown in FIG. 4, the DVD diffraction pattern PTd is formed concentrically in a range from the center to about 2/3 of the outer diameter on the lower surface of the diffraction element 20.

  In this way, in the lower layer portion 20B of the diffraction element 20, the DVD diffraction pattern PTd having a stepped shape is periodically formed on the DVD diffraction pattern layer 20F joined to the lower side of the base layer 20C. The beam is diffracted or transmitted according to the wavelength, and as a result, functions as a DVD diffraction grating DGd that diffracts only the DVD light beam Ld as the light beam of the second wavelength.

(2) Method for Manufacturing Diffraction Element Next, a method for manufacturing the diffraction element 20 will be described. As shown in FIG. 6A, in the diffraction element 20, a CD diffraction pattern layer 20D and a DVD diffraction pattern layer 20F are bonded to the upper side and the lower side of the base layer 20C, respectively.

  As described above, the base layer 20C is an injection-molded product manufactured by filling a mold with a transparent synthetic resin (for example, a polyolefin-based resin) having a predetermined refractive index, such as shrinkage when the resin cools. It is unavoidable that the distortion caused by. For this reason, in this diffraction element 20, by forming the diffraction pattern layer for CD 20D and the diffraction pattern layer for DVD 20F on the upper surface 20Ca and the lower surface 20Cb of the base layer 20C, respectively, the distortion of the base layer 20C is obtained. Are optically offset by the diffraction pattern layer for CD 20D and the diffraction pattern layer for DVD 20F, and the optical characteristics of the diffraction element 20 are kept good.

  That is, as described above, the base layer 20C has a distortion caused by injection molding, and therefore, the upper surface 20Ca and the lower surface 20Cb that should originally be flat also have a distortion. However, since the UV curable resin forming the CD diffraction pattern layer 20D and the DVD diffraction pattern layer 20F has a refractive index substantially equal to that of the base layer 20C, the CD diffraction pattern layer 20D and the DVD diffraction pattern are provided. The layer 20F and the base layer 20C are optically integrated so that the distortion of the upper surface 20Ca and the lower surface 20Cb does not have an optical effect.

(2-1) Formation of DVD Diffraction Pattern Layer When the diffraction element 20 is manufactured, first, the DVD diffraction pattern layer 20F is formed. That is, as shown in FIG. 7A, the first UV as a photocurable resin having a refractive index substantially equal to the injection molding resin for forming the base layer 20C on the lower surface 20Cb of the base layer 20C by injection molding. A cured resin 100A is applied.

  Subsequently, as shown in FIG. 7B, a UV curable resin 100A in which a DVD diffraction grating mold 101 having a mold shape obtained by inverting the DVD diffraction pattern PTd (FIG. 6C) is applied to the lower surface 20Cb. In addition, the ultraviolet light source (not shown) is used to irradiate UV light for resin curing from the upper surface side of the base layer 20C to transfer the first shape of the DVD diffraction grating mold 101A. As shown in FIG. 7C, the DVD diffraction pattern layer 20F accurately reproducing the DVD diffraction pattern PTd is formed in close contact with the lower surface 20Cb of the base layer 20C.

(2-2) Formation of CD diffraction pattern layer After the DVD diffraction pattern layer 20F is formed using the UV replica method, the CD diffraction pattern layer 20D is formed. The CD diffraction pattern PTc of the pattern layer 20D is different from the DVD diffraction pattern PTd of the DVD diffraction pattern layer 20F in that it is finer and has a larger aspect ratio.

  That is, as shown in FIG. 6C, the DVD diffraction pattern PTd has a total depth of 6 [μm] and a pitch of 170 [μm]. The total depth is shallow with respect to the pitch and the pitch itself is wide. Thus, the DVD diffraction grating mold 101A for forming the DVD diffraction pattern layer 20F can be easily and accurately produced by a wafer process using RIE processing.

  On the other hand, the CD diffraction pattern PTc has a total depth of 12 [μm] and a pitch of 10 [μm] (step width of 3.3 [μm]) as shown in FIG. Compared with the pattern PTd, the pitch is extremely narrow and the total depth is twice as large, and the entire pattern has a thin and deep pattern shape.

  Here, if the aspect ratio of the diffraction pattern is defined as “the larger of the two walls adjacent to the step / the step width”, the aspect ratio of the deepest step in the CD diffraction pattern PTc is 12 [μm. ] ÷ 3.3 [μm] = 3.6, which is a large value. Further, the total depth of the CD diffraction pattern PTc is 12 [μm], and in the wafer process using the RIE process described above, a mold for forming the CD diffraction pattern PTc cannot be formed with high accuracy. There is a problem.

  Specifically, as the processing depth by RIE increases, the shape accuracy such as wall verticality, bottom flatness, depth dimensional accuracy, edge sharpness, etc. in the mold shape deteriorates. The diffraction pattern formed by the UV replica method using the mold also deteriorates the shape accuracy and reduces the optical performance.

  In order to deal with such a problem, in the diffraction element 20 of the present invention, the CD diffraction pattern layer 20D is formed by dividing the CD diffraction pattern layer PTc by one step. Thereby, the mold shape depth of the mold can be reduced, and the mold can be accurately produced by using the RIE process.

  That is, when the CD diffraction pattern layer 20D is formed, first, as shown in FIG. 8A, the first UV curable resin 100A is applied to the upper surface 20Ca of the base layer 20C.

  Subsequently, as shown in FIG. 8B, a UV curable resin in which a CD diffraction grating mold first stage 102A having a mold shape obtained by inverting the first stage of the CD diffraction pattern PTc is applied to the upper surface 20Ca. While pressing against 100A, the mold shape of the first stage 102A of the CD diffraction grating mold was transferred by irradiating ultraviolet rays for resin curing from the lower surface side of the base layer 20C using an ultraviolet light source (not shown). In this state, the first UV curable resin 100A is cured, and as shown in FIG. 8C, the CD diffraction pattern layer first stage 20D1 accurately reproducing the first stage of the CD diffraction pattern PTc is used as a base. It is formed in close contact with the upper surface 20Ca of the layer 20C.

  Here, as described above, the first stage 102A of the CD diffraction grating mold 102A is obtained by inverting the first stage of the CD diffraction pattern PTc, so that the mold shape has a width as shown in FIG. 8B. 6.7 [μm] and depth width 6 [μm], and the CD diffraction grating mold first stage 102A can be accurately produced by a wafer process using RIE processing. The first stage 20D1 can be formed with good shape accuracy.

  After the CD diffraction pattern layer first step 20D1 is formed in this way, the groove portion is filled with the second UV curable resin 100B as the photocurable resin constituting the cover layer 20E (FIG. 6B). To do.

  That is, as shown in FIG. 8C, after applying the second UV curable resin 100B to the first diffraction pattern layer 20D1 for CD, for example, as shown in FIG. By pressing a transparent flat plate mold 101B made of a synthetic quartz flat plate against the second UV curable resin 100B, the second UV curable resin 100B is brought into close contact with the groove portion of the first diffraction pattern layer for CD 20D1, By irradiating ultraviolet rays through the transparent flat plate mold 101B, the second UV curable resin 100B is cured in a state where the groove portion of the first diffraction pattern layer 20D1 for CD is filled (FIG. 8E).

  Subsequently, the second stage of the diffraction pattern layer for CD 20D is formed. That is, as shown in FIG. 9A, after applying the first UV curable resin 100A to the first diffraction pattern layer 20D1 for CD in which the groove portion is filled with the second UV curable resin 100B, As shown in (B), the second stage 102B of the CD diffraction grating mold having the shape reversed from the second stage of the CD diffraction pattern PTc is pressed, and ultraviolet rays are irradiated from the lower surface side of the base layer 20C. Thus, the first UV curable resin 100A is cured in a state where the mold shape of the second stage 102B of the CD diffraction grating mold is transferred.

  Thus, as shown in FIG. 9C, the CD diffraction pattern layer second step 20D2 accurately reproducing the second step of the CD diffraction pattern PTc is laminated on the CD diffraction pattern layer first step 20D1. Thus, the CD diffraction pattern layer 20D including the first stage 20D1 and the second stage 20D2 is completed.

  As described above, since the second stage 102B of the CD diffraction grating mold is an inverted version of the second stage of the CD diffraction pattern PTc, the mold shape has a width of 3.3 as shown in FIG. 9B. [μm] and depth width 6 [μm], and the CD diffraction grating mold second stage 102B can be accurately produced by a wafer process using RIE processing. 20D2 can be formed with good shape accuracy.

  Here, when the CD diffraction pattern layer second stage 20D2 is formed by pressing the CD diffraction grating mold second stage 102B described above, the CD diffraction pattern layer first stage 20D1 is formed. The CD diffraction grating mold second stage 102B needs to be accurately positioned.

  As such a positioning method, for example, markings are made at appropriate positions on both the first stage 102A and the second stage 102B of the CD diffraction grating mold, and both the markings are matched with each other under a microscope. good.

  After the CD diffraction pattern layer 20D is formed in this way, the second UV curable resin 100B is applied to the upper surface of the CD diffraction pattern layer 20D as shown in FIG. 9C.

  Then, as shown in FIG. 9D, the transparent flat plate mold 101B is pressed away from the upper surface of the CD diffraction pattern layer 20D by a predetermined distance (for example, about 3 [μm]), and the transparent flat plate mold 101B is further pressed. Then, the cover layer 20E that covers the entire CD diffraction pattern layer 20D (that is, the entire CD diffraction pattern PTc (FIG. 6B)) flatly is formed (FIG. 9E).

  Here, when filling the CD diffraction pattern layer 20D with the second UV curable resin 100B in the groove portion of the CD diffraction pattern layer first step 20D1 (FIG. 8D), the CD diffraction pattern layer first Since the transparent flat plate mold 101B cannot be completely brought into close contact with the step 20D1, as shown in FIG. 10, the top of the CD diffraction pattern layer first step 20D1 and the CD diffraction pattern layer second step 20D2 In the meantime, the second UV curable resin thin film 100B1 is formed, and the CD diffraction pattern layer first stage 20D1 and the CD diffraction pattern layer second stage 20D2 become discontinuous by the thin film 100B1. .

  Similarly, when forming the CD diffraction pattern layer second stage 20D2 (FIG. 9B), the CD diffraction grating mold second stage 102B cannot be completely brought into close contact. As shown, the second UV curable resin 100B filled in the groove portion of the first diffraction pattern layer 20D1 for CD and the second UV curable resin 100B filled in the groove portion of the second diffraction pattern layer 20D2 for CD. In between, the thin film 100A1 of the first UV curable resin is formed, and the cover layer 20E also becomes discontinuous due to the interposition of the thin film 100A1.

  Such interposition of the thin films 100A1 and 100B1 can cause a reduction in the diffraction efficiency of the diffraction pattern PTc for CD. However, since the film thickness of the thin films 100A1 and B1 can actually be suppressed to 2 [μm] or less, The diffraction efficiency fluctuation at the wavelength can be kept within ± 0.5%, and the aberration is not affected.

(3) Operation and Effect In the above-described configuration, in the diffraction element 20, when the CD diffraction pattern layer 20D is formed using the UV replica method, the CD diffraction pattern layer 20D is formed as one stage of the CD diffraction pattern PTc. Each process was formed separately.

  For this reason, a mold for transferring the shape of the CD diffraction pattern PTc is divided into a CD diffraction grating mold first stage 102A and a CD diffraction grating mold second stage 102B. This improves the shape accuracy such as the verticality of the wall, flatness of the bottom, dimensional accuracy of the depth, and sharpness of the edge when a mold is created by RIE processing. Can do.

  Then, the CD diffraction pattern layer 20D is formed by using the CD diffraction grating mold first stage 102A and the CD diffraction grating mold second stage 102B created in this manner, whereby the CD diffraction pattern PTc. The diffractive element 20 having a high diffraction efficiency with respect to the CD light beam Lc can be manufactured.

  In practice, the diffraction element 20 manufactured using the first stage 102A for CD diffraction grating and the second stage 102B for CD diffraction grating according to the present invention uses a mold having a conventional integral mold shape. Compared with the diffractive element manufactured in this way, the diffraction efficiency improved by about 3%.

  According to the above configuration, the mold for transferring the shape of the CD diffraction pattern PTc is divided into the CD diffraction grating mold first stage 102A and the CD diffraction grating mold second stage 102B. Thus, the shape accuracy of the mold is improved, and by using these molds, the diffraction pattern layer for CD 20D is formed for each stage of the diffraction pattern for CD PTc, so that the diffraction accuracy is high and the diffraction efficiency is high. 20 can be obtained.

(4) Other Embodiments In the above-described embodiment, the case where the present invention is applied to a diffraction grating having two diffraction pattern stages has been described. The present invention can also be applied when manufacturing a diffraction grating having the above diffraction pattern.

  For example, FIG. 11A shows a CD diffraction pattern layer 20D in which the number of steps is increased to three (four steps) in order to obtain higher diffraction efficiency for the CD light beam Lc, and the CD diffraction pattern PTc3. Has a total depth of 18 [μm], a pitch of 10 [μm], and a step width of 2.5 [μm], and the step width is narrower than that of the two-stage CD diffraction pattern layer 20D shown in FIG. In addition, the total depth is deep, and the aspect ratio is 18 [μm] ÷ 2.5 [μm] = 7.2.

  Also when forming the CD diffraction pattern layer 20D having such a narrow and deep CD diffraction pattern PTc3, the mold is divided and prepared, and the CD diffraction pattern is formed as shown in FIG. If the CD diffraction pattern layer 20D is formed for each stage of PTc3, it is possible to reduce the mold shape depth of each stage of the mold and create a highly accurate mold, and this can be used to improve the shape accuracy. A diffraction grating having a good and high diffraction efficiency can be produced.

  FIG. 12A shows the CD diffraction pattern layer 20D with the number of steps increased to four (5 steps). The CD diffraction pattern PTc4 has a total depth of 24 [μm], a pitch of 10 [μm], and steps. The width is 2 [μm], the step width is narrower and the total depth is deep, and the aspect ratio is 24 [μm] / 2 [μm] = 12.

  Even when the CD diffraction pattern layer 20D having such a CD diffraction pattern PTc4 is formed, it is possible to create a highly accurate mold by dividing each stage. In the case of such a diffraction pattern layer having a large number of steps, the apparent aspect at the intermediate step is reduced, so that a plurality of intermediate steps can be formed together with a single mold.

  That is, like the CD diffraction pattern layer 20D shown in FIG. 12B, the uppermost stage and the lowermost stage (CD diffraction pattern layer first stage 20D1 and fourth stage 20D1) are formed one by one, and the intermediate stage. Even though the CD diffraction pattern layer second and third steps 20D23 of the CD are formed in two steps, the bottom width and the top width of the second and third steps 20D23 for CD diffraction pattern layer are step widths 2 [μm]. Therefore, the aspect ratio becomes the same as that of the first diffraction pattern layer 20D1 for CD, thereby making it possible to create a mold having good shape accuracy.

  Furthermore, depending on the pattern shape of the diffraction pattern, first, a plurality of steps may be formed from the lowest step of the diffraction pattern, and then the remaining steps may be formed. The mold may be divided into stages.

  Furthermore, in the above-described embodiment, the second UV curable resin 100B that forms the cover layer 20E is filled into the grooves of the diffraction pattern layer one step at a time using the transparent flat plate mold 101B. The present invention is not limited to this, and if the cover layer 20E is also formed in a step shape using a mold having a shape corresponding to the diffraction pattern, the total number of steps can be reduced.

  That is, as shown in FIG. 13 (A), the first UV curable resin 100A is first applied to the surface of the base layer 20C, and then the diffraction layer mold first having a mold shape in which the first stage of the diffraction pattern is reversed. The first UV curable resin 100A is transferred in a state where the mold shape of the first stage 201A of the diffraction layer mold is transferred by pressing the step 201A and irradiating ultraviolet rays for resin curing from the lower surface side of the base layer 20C. Curing is performed to form the first diffraction pattern layer 20D1 in close contact with the upper surface of the base layer 20C (FIG. 13B).

  Subsequently, after the second UV curable resin 100B is applied to the upper surface of the diffraction pattern layer first step 20D1, the shape of the cover layer is reversed (that is, the same shape as the second step of the diffraction pattern layer). The first layer 201A of the cover layer mold 201A is pressed, and the mold shape of the first layer 201A of the cover layer mold is transferred by irradiating ultraviolet rays for resin curing from the lower surface side of the base layer 20C. Then, the second UV curable resin 100A is cured to form the cover layer first and second steps 20E12 in close contact with the upper surface of the diffraction pattern layer first step 20D1 (FIG. 13C).

  Then, after the first UV curable resin 100A is applied to the upper surfaces of the cover layer first and second steps 20E12 and the diffraction pattern layer first step 20D1, the diffraction layer has a mold shape in which the third step of the diffraction pattern is reversed. By pressing the mold second stage 201B and further irradiating the resin curing ultraviolet rays from the lower surface side of the base layer 20C, the first UV is transferred in a state where the mold shape of the diffraction layer mold second stage 201B is transferred. The cured resin 100A is cured to form the second and third diffraction pattern layers 20D23 in close contact with the upper surface of the first diffraction pattern layer 20D1 (FIG. 13D).

  Further, after the second UV curable resin 100B is applied to the upper surfaces of the cover layer first and second steps 20E12 and the diffraction pattern layers second and third steps 20D23, the cover layer mold second step 202B having a flat plate shape is pressed. Further, the cover layer first and second steps 20E12 and the diffraction pattern layer second and third steps 20D23 are covered in a flat state by irradiating ultraviolet rays for resin curing from the lower surface side of the base layer 20C. The UV curable resin 100B is cured to form the cover layer third stage 20E3 (FIG. 13E).

  Thus, the diffraction pattern layer first step 20D1, the cover layer first and second steps 20E12, the diffraction pattern layer second and third steps 20D23, and the cover layer third step 20E3 are sequentially formed by performing the replica process four times. The diffraction pattern layer 20D is composed of the first diffraction pattern layer 20D1 and the second and third diffraction pattern layers 20D23, and the cover layer is composed of the first and second cover layers 20E12 and the third cover layer 20E3. 20E is formed.

  When the diffraction grating is formed by such a process, a thin film of UV curable resin as shown in FIG. 10 is formed between the respective steps of the diffraction pattern layer 20D and the cover layer 20E as shown in FIG. There is also an advantage that there is nothing.

  The present invention can also be used in various optical elements that use light beams having a plurality of wavelengths.

It is an approximate line figure used for explanation of metallic mold creation by a wafer process. It is a block diagram which shows the whole structure of an optical disk device. It is a basic diagram which shows the structure of an optical pick-up. It is a rough-line perspective view which shows the structure of an objective lens unit. It is a basic diagram which shows the optical path in an objective lens unit. It is a basic diagram which shows the structure of a diffraction element. It is a basic diagram which shows the formation method of the diffraction pattern layer for DVD. It is a basic diagram which shows the formation method of the diffraction pattern layer for CD. It is a basic diagram which shows the formation method of the diffraction pattern layer for CD. It is a basic diagram with which it uses for description of the thin film formed in the diffraction pattern layer for CD, and a cover layer. It is a basic diagram which shows the structure of the diffraction element of other embodiment. It is a basic diagram which shows the structure of the diffraction element of other embodiment. It is a basic diagram which shows the structure of the diffraction element of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 7 ... Optical pick-up, 9 ... Objective lens unit, 20 ... Diffraction element, 20A ... Upper layer part, 20B ... Lower layer part, 20C ... Base layer, 20D ... Cover layer, 20E ... Diffraction pattern layer for CD, 20F ... Diffraction pattern layer for DVD, 21 ... Objective lens, DGc ... Diffraction grating for CD, DGd ... Diffraction grating for DVD, DG ... Diffraction grating, PTc ... For CD Diffraction pattern, PTd: diffraction pattern for DVD.

Claims (10)

A diffraction pattern formed by pressing a mold against a photocurable resin applied to one surface of a base member and curing it to form a multi-step diffraction pattern on the opposite surface of the surface in contact with the base member With layers,
The diffraction pattern layer is formed by being divided into a plurality of layers for each step of the diffraction pattern. 2. A cover layer provided in close contact with the diffraction pattern of the diffraction pattern layer and formed of a second photocurable resin having a refractive index different from that of the photocurable resin. The diffraction element described in 1. The cover layer is
Each time a part of the diffraction pattern layer is formed, the second photo-curable resin is applied to the surface of the part of the formed layer, and then a flat metal mold is pressed and cured. The diffraction element according to claim 2, wherein the second photocurable resin is sequentially filled by filling the groove portion of the formed layer. The cover layer is
Each time a part of the diffraction pattern layer is formed, the second photocurable resin is applied to the surface of the part of the formed layer, and then one of the diffraction pattern layers to be formed next. By pressing and curing a mold having the same mold shape as the groove shape of the part layer, the second photo-curing resin is filled in the groove part of the formed layer and then formed next. The diffraction element according to claim 2, wherein the diffraction element is sequentially formed by curing in a shape corresponding to the groove portion of the layer of the portion. The diffraction element according to claim 1, wherein the mold is formed using silicon as a base material. In the method for manufacturing a diffraction element, on one surface of the base member, a diffraction pattern layer having a diffraction pattern having a plurality of steps formed of a photocurable resin is provided.
By pressing and curing a mold having a mold shape obtained by inverting the shape of some steps including the lowest step of the diffraction pattern against the photocurable resin applied to one surface of the base member, the diffraction is performed. Forming a part of the pattern layer;
A gold mold having a shape obtained by inverting the shape of all or some of the unformed steps in the diffraction pattern with respect to the photocurable resin applied to the surface of a part of the formed diffraction pattern layer. Forming a remaining all or a part of the diffraction pattern layer by pressing the mold and curing the mold. The cover layer is formed by adhering and curing a second photocurable resin having a refractive index different from that of the photocurable resin to the diffraction pattern of the diffraction pattern layer. A method for manufacturing a diffraction element. Each time the partial layer of the diffraction pattern layer is formed, the second photo-curable resin is applied to the surface of the formed partial layer, and then the flat mold is pressed and cured. The method for manufacturing a diffraction element according to claim 7, wherein the groove layer of the formed layer is filled with the second photocurable resin to sequentially form the cover layer. Each time the partial layer of the diffraction pattern layer is formed, the second photocurable resin is applied to the surface of the formed partial layer, and then the partial layer of the diffraction pattern layer to be formed next. The mold having the same shape as the groove shape is pressed and cured to fill the groove portion of the formed layer with the second photocurable resin, and to form a part of the next layer The method of manufacturing a diffraction element according to claim 7, wherein the cover layer is sequentially formed by curing in a shape corresponding to the groove portion. The method for manufacturing a diffraction element according to claim 6, wherein the mold is formed using silicon as a base material.

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